Lead overcharging

[biscuit]

I have set a charger to charge my AGMs at 28.8V for 8 hours before dropping to 26.6V. That is the best I can do with that charger, as it has no option to set a termination current. Otherwise it goes to float at 27.8V after about 3 hours. I do not believe that this is enough time for a good charge.

I could maybe set it to 5 hours, on the basis that the PL8 has been known to take about that time to reach termination current on the old batteries in that chair. But these are not the same batteries, so I made a guess about how long will do.

My question is, if 8 hours is too long, what happens? Does the current simply drop to 0A and stay there? Or will the charger "force-feed" it current in some way? Are there any symptoms to show whether my batteries are suffering?

[Burgerman]

What termination current are you setting?
If a deep cycle battery is fully discharged, it will take around 8 to 10 hours at its CV current to reach around 1/500th to 1/1000th of its capacity. So that would be for a 100Ah battery, fully discharged, around 8 to 10 hours if charged at around 10A or 15A. The current will take that long to drop to the correct "full" charge figure. What is that figure? 100Ah div by 1000 is 1 tenth of an amp. Not all batteries will ever reach at low. So we limit this to 8 hours at CV so maybe 11 hours to 14 hours depending on initial charge rate.

If the battery is only 50% discharged, as is common, it will shorten the initial bulk stage by half. And then it may take 8 hours at CV but 8 is safe. As long as the current is still low. Say under an amp at this point. But if its still dropping, then keep going!

If its only 25% discharged, then it will soon go to its CV stage and current starts dropping. It will still take around 7 hours or so at CV.

If its nearly full, say 10% discharged, then it may take 6 hours OF CV and then reach the 500th to 1000th point. We dont know which. It depends on battery, type, history, temperature, actual CV stage voltage etc. Its charged when it only drops by under 1/10th of an amp over 1 hour. Its still safe at 8 hour limit. But here it may be better to do 6 hours and then to float. These were around 70% discharged.

If its already 99% charged, it STILL takes around 3 to 5 hours to top off... Its charged when it stops falling!

Can too long at CV hurt?
Yes. But its not as bad as not long enough. PROVIDED that the current is low. Like say .2 of an amp then its no real issue. The battery would if you repeatedly did this end up with no sulfation, but positive grid corrosion. If you undercharge it you will end up with sulphation, and less grid corrosion...

The other thing to consider is that of electrolyte loss. Our batteries are valve regulated. A battery begins to gas (turn the water into hydrogen and oxygen) ony when the thing is charged, and or when the voltage is above a safe value. The recombination only happens slowly. So if you charge at too high volts then the gassing esxceeds the recombination speed. And this also consumes energy and warms the battery. If its below an amp, and only happens for an hour or two on a AGM its not a problem. If you are at a few hundred mA then its still not a problem. If you charged at say 15 volts, and then left it going for 8 hours CV when it didnt need it then there would be a problem But we dont.

This electrolyte bubbling when charged and when at a higher voltage is much more of a problem for gel. They cannot recombinne the gasses back into water as fast, and it causes electrolyte losses and the gel dries out or shrinks. And the bubbles cause voids. Which is why we use a lowr voltage.

So if your battery is almost full, you can charge for say 5 to 7 hours CV. If its had normal 8 hours of use then even if only indoors, 8 hours will probably not be enough and the float will finish the job. Its a happy medium.

This is why we say in CYCLIC use, 1000thC terminaton or 8 hours whichever occurs first. Remembering that some batteries may need some adjustment to that 1000thC like maybe 500th? It all depends. If you dont know what battery you are designing a charger for, its "safer" to set it to stop charging after around 4 or 5 hours, and rely on float to finish the job. But thats what mobility chargers do. And the problem with that is that it takes an age for float to finish a charge. Like it may take an extra 7 to 10 hours. So for cyclic use its a daft way to do it. Users end up trusting that green light and getting up and going out. When its not really charged fully. But they cant know that. If they did, they wouldnt be happy.

Look at how long it REALLY takes to charge even at full CV voltage below.

This isnt actually finished. It is 2x 70Ah Odyssey batteries in parallel. Now that means 140Ah So it will end at 140mA (1000thC). This is where the 8 hours approx CV time comes from. These are charging at 30A. Remember that Odyssey charge faster than almost all other batteries due to low impedance, pure lead technology and strong electrolyte.

Aps dropping away here black graph, odyssey. White graph MK gel, and thats not close to being done. Even at a 12A XLR charge. After 11 hours. How am I supposed to get up?

[Burgerman]

When you say you SET A CHARGER and it ends at 3 hours. Then float, what is that charger? Because unless that battery is already full, thats wrong. Unless you want to wait 10 more hours on float?

[martin007]

I have set a charger to charge my AGMs at 28.8V for 8 hours before dropping to 26.6V. That is the best I can do with that charger, as it has no option to set a termination current. Otherwise it goes to float at 27.8V after about 3 hours. I do not believe that this is enough time for a good charge.

I could maybe set it to 5 hours, on the basis that the PL8 has been known to take about that time to reach termination current on the old batteries in that chair. But these are not the same batteries, so I made a guess about how long will do.

My question is, if 8 hours is too long, what happens? Does the current simply drop to 0A and stay there? Or will the charger "force-feed" it current in some way? Are there any symptoms to show whether my batteries are suffering?

You don't have a Shirley charger?

[Burgerman]

Yes she has and its in bits...

[martin007]

in bits?

[biscuit]

It's the Victron I have set to 8 hours. Left to its own devices, the Victron floats when it decides to, otherwise. The ZXD is in pieces still and I am not getting any niftier, it turns out. Disability isn't cheap!

You can't set a termination voltage on the Victron. You can make it do a fixed absorption time or you can endure its adaptive absorption time. That is the choice. Its display rounds to 1/10A. My batteries are 35Ah.

[Burgerman]

The victron floats only when you ell it to do so IF YOU PROGRAM IT PROPERLY!

You have some of its "smart" stuff enabled. I have the software on my PC and can configure it properly but its hard as they hide things descretely. In several places and it tries to go back to their defaults as you proceed to set it. You just have to be paying attenton.

35Ah should terminate at around 35 to 70mA. So set it to 50 to test. If you cant or it never reaches that set it to the closest so 0.1A (100mA) and test that. On the victron you just have to rely on 8 hours. Have 2 profiles.

1 set with their variable absorption. For topping up a almost full battery. Set their stupid recondition thing to off. If it wont allow that set it to the longest period like weeks or months... You have to allow their float stage to finish the actual charge.

2 set one to 8 hours plus float at 13.6V and long term float at 13.35V. Without their safety nazi intelligent nonsense trying to out think you. Use his 8 hour profile any time the battery has actually gone say 1/4 of a mile or more. Or been used for half an hour indoors.

Note...
The reason to get it to termnate at a low current rather than stopping CV early is SPEED OF CHARGE. If it ends after 8 Hours CV or at say 1000th of capacity is because NO FLOAT IS REQUIRED. Its completely charged when CV ends. Thats a lot faster for our cyclic use.
IF it ends early, say at 1A, then goes to float, it takes MANY HOURS LONGER before the charge is complete. Since no fine tuning is needed here most chargers do this... Inc the viscton. And all mobility chargers.

So if termination current is 8 hours CV or 1000 (or 500th?) of capacity then a TWO STAGE charge is all thats needed.
If not, then an extra float stage is needed (3 stage) which takes a lot lot longer as at this lower voltage also drastically reduces charge current since its only slightly above the battery voltage.
And so the earlier it stops CV the longer the float stage will be.

The PL8 is a charger. Not a maintainer. It allows complete charge, by using a low adjustable termination current fine tuned to the battery. And an 8 hour CV timer. It doesent do float at all then, and it doesent need to.

[shirley_hkg]

I bought 8 cells for only £158 last week. They deliver 150Ah effortlessly. (internal resistance @0.3mΩ, pack's volt bounced back to 24.983v in half an hour).

LiFePO4 price dropped so significantly, that we have no reason to linger around SLA anymore at all now.

Thank you for helping me the trip to London last September, biscuit. I can make you all wiring harness with a LiFe pack for FREE. My sister-in-law returns to Birmingham next month. Free shipping then.

[shirley_hkg]

This flutter is nothing but I slowed it down to 150mA(from 25.5A) to get the pack's voltage (unloaded) when it was 110Ah discharged. I have to tell the user when to recharge his pack at this voltage not loaded.

[Burgerman]

If interested, that will give you over 3x the range - maybe a little more - compared to a set of 75Ah lead bricks. And weight less than half as much. And last at least a decade if not two.

You will then experience what its like to have no limits. You learn after a week or three that after a busy day you only used 1/4 of it... And so lose the mental conditioning that prevents you from going much, much further. No more range anxiety built into your brain.

[biscuit]

Shirley - that is a very kind offer. I will pm you. My battery space is limited, two boxes sitting on a folding steel grid tray. Your SIL need not be burdened, if we can find a way to make this possible.

I am glad your journey worked out. I was worried, especially about you taking a train on a Sunday.

Burgerman - thank you, it was a very good clear explanation.

I programmed the Victron. It was reluctant, with options hiding behind warnings. They did not actually use the words 'Hands off, fool', but the meaning could be inferred. It is an annoying machine, for example, counting down its cycle tally, a very stupid way to keep count.

[Burgerman]

With lead, I change charge parameters all the time. By estimating whats needed as it varies, and watching the charge happen. When its done I stop it. When in a hurry, I charge at a higher rate with no float, and do 2 stages. When no hurry I charge at a few tenths of a volt less which takes longer, and leave it on float voltage of 13.8 for a few hours. Or 13.6 for maybe 12 hours. Or 13.35 indefinitely. And so on. With older or sulphated batteries, and some brands the termination current has to be hgher or charge voltage lower... I watch what happens and adjust accordingly.

As you can see theres no one size fits all. UNLESS you:
a) dont care how long they survive (over voltage, undercharging mobility chargers and cheap one size fits all chargers generally)
b) you have 16 to 20 hours to allow a early cut off from CV and a really l o n g float stage to get it from 95% to 100. Again most mobility chargers do this. But give a green light at the end of CV long before that essential last couple of percent is in there. So they think its done after 4 to 5 hours! This results in sulphation from undercharging long term.

Charging lead properly in a short overnight time period is pretty difficult. And needs manual fine tuning to match your battery and usage.

Lithium on the other hand charges much much much faster! Since you can charge at max speed, full amps, for 99% of the charge. And hey dont care if you never complete the charge! In fact they benefit from it.

[biscuit]

The battery would have a very easy life in my case. I get too fatigued to go on long rides. In fact as it stands I don't usually use the chair at all until three days later.

I have to measure the battery space. I am presently lying down indoors, while the chair is in the garage.

That devilish Victron does a float, like it or not. It has no option to set a float time, though one can set a float voltage. I have set it to the same voltage as storage, i.e. 26.8V, and it will do storage indefinitely (maybe actually a week is the default, but I could choose how long before it does another absorption cycle) as soon as it decides we have done enough floating.

[Burgerman]

It has no option to set a float time, though one can set a float voltage.

Where you have a float that can be set at 2 different voltages it is used to finish a too short CV stage charge, one where it isnt actually full, and then to hold the battery at the safe very slow charge for a bit.

So it SHOULD go to float at say 13.6 or 13.7 (double this for 2 series) for a while. Maybe a few hours or so. Then after this has completed the charge, i should drop to a lower float value of 13.3 to 13.4V (again double that) indefinitely. Theres no reason to repeat that absorption (CV stage) at all. Ever. Unless something has pulled the battery down low. Like in a car with some lights left on for e.g. So set that to never/as long as humanly possible. Its a pain. All that will do is try and charge a full battery.

[biscuit]

Yes. It wasn't me that had that idea, it was messrs. Victron. The float time is adaptive depending on the absorption duration, the user cannot touch it. But we can choose the voltage, so I did that, I made it there same as the storage voltage to take into account the long absorption. The default float voltage was 27.6V.

[Burgerman]

Thats OK for safe charge after the CV. Just not for more than a day. So best to put it back! No gassing at that voltage or better still at initial float 13.6/7 volts. x2.

As long as the float voltage is a safe one, which it is, it is fine even after a long CV time. Because no significant gassing should occur at this lower voltage.

Why is the ZXD in bits?

[biscuit]

It is too embarrassing to explain! But...
On about day 1 after it arrived, I tripped up (a Thing that happens to me on good days) while carrying it to the plug, dislodged the display screen while it flew out of my hands (another Thing) so I had less than no clue what I was doing, so I reckoned I'd take out those itty bitty screws to try lining things up again and while I'm about it, take a gander at what goes into these machines... Bad to worse. I live in hope that some day I will resurrect it and programme it. There is a thread about programming the ZXD oh here somewhere that I could follow.

Fact is, I have a cheap and nasty wheelchair (nasty I have been told, anyway, but I like it) with pathetic little batteries that always either have just been replaced or need replacing soon. And, to my surprise, I have found that I enjoy venturing to the interior of these objects that I have to make room for in my life. I am usually a bit slow on the uptake and do a lot of daft things.

Anyway. Enough excuses for my crazy ways.

[biscuit]

Ermm... Do you mean I should let the Victron do its defaults, which are
adaptive absorption time at 28.8V ( likely 2 hours or so)
then adaptive float time at 27.6V (same)
then storage time at 26.2V

The Victron gets its knickers in a twist if you try changing things while it is busy. It may allow me to create a preset without returning to the start of the charge cycle, or it may not. It may flick over to the 29.4V cycle, or it may not. That "high" cycle is why I even made a preset in the first place. I thought maybe it does a bulk stage of 29.4V followed by the advertised absorption stage at 28.8V. Now I think it got confused, as it does.

[Burgerman]

No I mean set a 2 stage float in your custom profile.

bulk stage of 29.4V

Theres no such hing as a bulk stage at ANY particular voltage. Bulk is als called CC or Constant Current. It is when you connect the charer and it hits the battery with its full maximum amps. At this point the battery voltage climbs slowly until it reaches the CV (Constant Voltage) stage also called absorption by retards! As it holds this CV steady at whatever you set the battery itself pulls less and less amps in a big curve that takes between 6 and 12 hours typically depending on how discharged ot was.

The middle one shows what happens if you cut the CV stage short at 4 hours. It is showing that the current was still high and still charging slowly. These are all just drawing to help people understand. The PL8 draws the same graphs from REAL batteries under charge.

[Burgerman]

PL8 2 stage...

[Burgerman]

Matching volts...

The slope at the start where it hasnt reached the 14.7V point, is CC or Bulk.

[scottnj@gmail.com]

I'm curious about the ProMariner ProSport dual bank chargers. Would these be good for long term storage for a backup chair that rarely gets used. It has MK Gel Group 24s that already have powerpoles attached, so easy to hook up directly to the batteries.

The ProSport chargers have profiles for wet, gel, and agm. I just don't know how good the profiles are for our batteries.

They have them in 8 through 20 amp versions.
https://www.promariner.com/en/p/44008/ProSptHD-8-8-Amps-2-Bank

[Burgerman]

Post the charge algo that they do here and I can tell you.

If they charge at a CV (absorption) stage of 14.1 or 28.2V for gel, and float at say 13.5 to 13.8V then thats great for charging. And they should take around 10 hous or so to achive a full charge. And up to 1 or 2 days max. The float charge is too high for longer periods.

However for LONG TERM float you need a low float CV voltage of 13.3 to 13.35V indefinitely. At this voltage they will last as long as its possible to make them survive while not in use.

Alternatively you can DISCONNECT a cable so that the battery is not connected to a chairs power module. Or just disconnect via the breaker if it has one. urning the chair off at the joystick is not enough. And then just give a normal charge every 2 to 4 weeks. This will also make them last a long long time.

[scottnj@gmail.com]

This is the best info that I can find.

GEL: 14.1VDC Absorption, 13.8VDC Float

There's a chart on this page, but I couldn't figure out how to post it here from my phone. Here's a link.

https://www.promariner.com/en/products/Waterproof-On-Board-Battery-Chargers/ProSport-Series/ProSport-HD

Fully Automatic Charge Profile
The ProSportHD is designed for all 12 Volt Flooded (Lead-Acid), AGM and Gel batteries.
After completing the installation of your new ProSportHD Charger and with no wiring or connection
errors, the battery(s) connected are greater than 2.5VDC and can accept a charge, the ProSportHD
will sequentially perform the following 5-Stage Digital Performance Charging Process. If your
battery(s) are full, the charger will start maintaining your batteries immediately after it finishes
analyze mode.
5 Stage Performance Charging Overview
Stage 1 - Analyze & System Check OK: During this stage the ProSportHD Mode LED will
pulse blue indicating it is analyzing all battery connections and ensuring each battery is capable
of being charged. When completed successfully, the System Check OK indicator will illuminate
green. This takes approximately 1 minute.
Stage 2 - Charge: During this stage the ProSportHD Mode LED will be solid red and the
ProSportHD will use all of its available charging amps (as controlled by temperature) until the
battery voltage is raised to the selected Battery Types absorption voltage (see page 14).
Stage 3 - Condition: During this stage the ProSportHD Mode LED will be solid amber and
the ProSportHD will hold all batteries at the selected absorption voltage to complete charging
while conditioning each battery connected for up to 3 hours as needed.
Stage 4 - Auto Maintain (Energy Saver Mode): During this stage the ProSportHD’s Mode
indicator will be solid green, indicating it is monitoring and auto maintaining your batteries when
needed to maintain a full state of charge. At this time, the blue Power LED, green System OK
and green Mode LEDs will remain on letting you know your batteries are ready when you are.
Stage 5 - Storage Recondition: During this stage the ProSportHD will enter into its once a month
Storage Recondition mode. The green Mode LED will pulse indicating, while your batteries / boat
are in storage, the ProSportHD is reconditioning all batteries for up to 3 hours once a month to
extend battery life and provide maximum reserve power performance on the water.

[Burgerman]

13.8v float is best for charging. But too much for long term stoage. You would need the 20A dual gang one too. Its intended for use on a back that is in use in a boat so always topping up during the day rather than being stored unused.

See these extra nonsense and potentially damaging stages? We do not want that!

Stage 3 - Condition: During this stage the ProSportHD Mode LED will be solid amber and
the ProSportHD will hold all batteries at the selected absorption voltage to complete charging
while conditioning each battery connected for up to 3 hours as needed.
Stage 4 - Auto Maintain (Energy Saver Mode): During this stage the ProSportHD’s Mode
indicator will be solid green, indicating it is monitoring and auto maintaining your batteries when
needed to maintain a full state of charge. At this time, the blue Power LED, green System OK
and green Mode LEDs will remain on letting you know your batteries are ready when you are.
Stage 5 - Storage Recondition: During this stage the ProSportHD will enter into its once a month
Storage Recondition mode. The green Mode LED will pulse indicating, while your batteries / boat
are in storage, the ProSportHD is reconditioning all batteries for up to 3 hours once a month to
extend battery life and provide maximum reserve power performance on the water.

It may be that it doesent do these recondition things to gel? Cant tell. But these things are not wanted.

We need 3 stages.
1. CC (BULK) at whatever current your charger can do or your XLR can handle or up to around a max of 24A on the 74Ah MK gel which is best.
2. CV (ABSORPTION) which is designed to hold voltage steady for approx 8 hours in cyclic use, or until current stos falling and is very low.
3. Float (to complete charge, a high float is best like 13.8V. To keep a battery healthy a lower 13.35V is perfect long term)

The victron chargers can be programmed to do both of these float levels. It will drop to 13.7 or 13.8 for a short while to complete charge and can be set to drop to 13.35V for long term storage. But you will need to set up a completely custom charge profile. The one you want is either the 12A or the 8A one. Or bigger if connected by Andersons.

[thetascott]

I noticed the Victron app kills my phone's battery so modified my settings not long ago to make it mostly plug and play.

I turned off their Adaptive charging and set the CV duration to Fixed for 1 hour and set the re-bulk current to 0.4. I use the following voltages for MK gels:

Aborption: 28.2
Float: 27.6
Storage: 27.2

This is for my primary chair used daily. Would use different settings for a backup chair.

If the current in the float stage exceeds 0.4 for a few seconds, it starts a new charge cycle with 1 hour at CV. It repeats until the float current stays at 0.4 or under. It has been working perfectly so far. It stays in the float stage for 8 hours but usually unplugged a bit before then.

I turned off the temperature compensation and adjust the voltages manually; it's easy. The Victron manual states that temperature compensation is not used if the temp. is above 25C and that's true. When a rebulk occurs, the internal temp. sensor obtains a temp. that exceeds 25C due to the heat produced by the charger and it uses the voltages entered as is. This will result in over-voltage during warmer months.

[Burgerman]

As long as you have at LEAST 16 hours available to charge each time that will work.
If not then it will result in undercharging and sulfation in cyclic use where we have only 8 hours to achive a 101% recharge in a limited time.

The battery will charge fully in around 20 hours to 24 hours at 13.8V.
The reason we use 14.1V as the slightly elevated voltage is that it basically halves the time taken to achieve full saturation. We cant use more because it causes problems with gel, in that it isnt as fast at recombination as a AGM or wet acid battey and so it causes bubbles and drying (shrinkage) in the gelled electrolyte that doesent recover. The reason that we would use less, like 13.8V to charge in a backup or float charge situation is because it increases the lifespan, but not by much. And its much slower owards the end.

So in an ideal cyclic use world you would maintain the battery at 14.1 volt (corrected to the BATTERY temperature) until current fails to drop by more than 0.1A over any 1 hour period, or around 12 hours absolute maximum, or until its curent falls to around 1/500th to 1/1000th of the 20h rate capacity. Whichever occurs first. And thats it. No float required. You can get up!

MKs temp correction: To compensate for battery temperature not at 20°C, subtract 0.005 V/cell for each 1°C above 20°C; add 0.005 V/cell for each 1°C under 20°C.
NOTE that this is BATTERY temperature. Not room temperature. Or charger temp. The battery may be 3 or 4 degrees warmer than the room.

This is the fastest way to achieve a complete charge in a limited period. Why is it important to achieve a absolutely fully saturated charge? Because as a battery discharges it takes the acid from the electrolyte, splits it (it gets closer to water) and coats the plates with lead dioxide and lead sulfate. As you charge to 100% which takes a long time, the sulfate is gradully all returned back to the electrolyte. If it isnt, and if even 1% is left behind every charge, then this turns to larger crystals that no longer conduct and cant ever be reversed. Time being important here (So recharge as soon as poss!). So you lose 1% capacity every charge this way. And this increases internal resistance too. So getting a really complete charge every cycle matters if you want to maximise cycle lifespan.

There is a even faster way.
That involves an accelerated finishing stage. At fixed current for a limited period once current drops to a certain point. (Rather than waiting 8 hours at CV to really low currents).
Typically 1A for 2 hours at the end of CV charge. This is normally used for airport cleaning machines etc. Where they generally try to get a full charge in 1 shift over 8 hours. This works because the amount of gassing it causes is limited in volume for a fixed period. So doesent cause enough gassing to pressurise the battery enough to lose electrolyte when done properly.

Whatever you do, a higher initial bulk charge of around 1/3rd the battery capacity in amps alows longer for the stupidly slow CV stage to complete. So charge at 12A via XLR or up to 25A via Andrson for best results.

http://www.wheelchairdriver.com/MK1.pdf MKs charge algo specs.

You should turn all the automated nonsense off on the victron. Esp recondition, and adaptive CV time and set CV to 8 hours in cyclic use. And float to 13.7, store to 13.35.

[Burgerman]

Heres a almost new MK gel battery on a 12A charge. By PL8. It is set to end when full, at 750th of capacity. Or8 hours CV whichever occurs first. So its current is still dropping here and not yet completely charged.

So far 11 total hours... With a 14.1 (28.2 series) charge. 100% FULL IS IMPORTANT! These were pretty well discharged. But it cannot be rushed.

Remember in cyclic use that if your charger says DONE before say 10 to 12 hours has passed it is not full.

[Burgerman]

Tps from MK, (MK gel pdf tech file):

Follow these tips for the longest life:
• Avoid deep discharges.
• Don’t leave a battery at a low stage of charge. Charge a discharged battery as soon as possible.
• Don’t cycle a battery at a low state of charge without regularly recharging fully.*
• Use the highest initial charging current available (up to 30% of the 20-hour capacity per hour) while staying within the proper temperature-compensated voltage range.

*Which basically means 14.1V in a normal room temperature that YOU are comfortable in, at 25A (via anderson), with 8 hour of CV so around an 11 hour total charge to completion.
If charging slower like say 8A via XLR then this adds approx around 2 to 3 hours to CC (INITIAL BULK STAGE) depending on discharge depth. So total charge will be around 16 hours in cyclic operation. CV stage may be slightly shorter.

___________________
A tip from me:

Charging fully at night is essential regardless. But to gain a huge boost in service life (and range!) a boost of an hour or so of charge during the day to decrease average depth of discharge helps enormously. Charge for a bit as you eat or check email etc. This works better at high current - I use my bench supply while sat at my PC before going out in the evening. Set to 28.2V and 25A usually. Or at 40A if it is already low, or I if have a long way to go to a specific town pub or resturant! I disconnect when it drops below around 5 to 8A. At high current it soon wacks some energy back in.
I need to be sure that I:
a) dont run them low (kills batteries fast) so low average depth of discharge to extend life.
b) that I dont get stranded on the way home at midnight... Even an XLR connected 8A mobility charger boost during the day helps some, its just too little and too slow really. How long have you got?

Doing this every day will make a battery that will normally die from heavy use in a year, last five years. Charging properly also helps enormously. The two things used together transforms battery lifespan beyond recognition.