PINNED - HOW to choose a LEAD BATTERY

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PINNED - HOW to choose a LEAD BATTERY

Postby Burgerman » 20 May 2015, 09:56

http://www.wheelchairjunkie.com/forums/ ... #Post66847
Junkie forum link.

THIS scenario above is **EXACTLY** why internal resistance, matters. And why all battery meter "fuel gauges" are so completely useless. It READ 37% charge quite correctly...
Still it wont go in his van... Because voltage falls too low under sever load, climbing the vans ramp when discharged to 37%. Because the battery resistance increases with the discharge level. In other words, 37% will work only on flat ground!

Its why I use ODYSSEY 2.5mOhm batteries instead of 4.5mOhm MK Gel (or any of the countless cheap & nasty 5 to 8mOhm AGM batteries that are even worse). They have HALF the resistance, and are twice as good as MK and 3x better than say these commonly installed cheap gel batteries: http://sigmastek.com/files/specsheets/SPG12-75(IT).pdf These Sigmastek batteries are typical, and have a massive 8mOhm internal resistance. I wouldn't use this in my grandmas nursing home chair.

All lead batteries are pretty much crap. Even the very best. But Odyssey is 2.5mOhm int resistance so is TWICE AS GOOD as 4.5mOhm MK gel, meaning its only half as crap at getting up the ramp... (That's a quite literal 2x as good under load). CHEAP GENERIC 7mOhm to 12mOhm from a typical AGM Chinese battery is some FOUR TIMES (4x) worse at times of heavy demand as the Odyssey is. And this still 2x worse than the quality MK gel.

Remember that the CLAIMED battery resistance gets worse as the battery discharges. So most batteries feel good when full.
So the Odyssey will be reduced from its excellent 2.5mOhm to just 5mOhm by the time its discharged.
But batteries that start off at 5mOhm feel a bit flat when they are still full! And get much worse as you drive.

Want a good battery for a wheelchair?
Then do this.
Look at FULL specs in this order:

1. Look for mOhm rating FIRST. (LOW is best).
2. Look for CYCLE LIFE at 80% discharge level. (400 to 550 acceptable - more is best)
3. Look for the largest battery CASE size you can fit in the space available.
4. Look at Ah very LAST of all! Its the least important.

Why? A 100Ah battery that feels "dead" and that cannot propel the powerchair after you used just 50Ah is no use at all.


This is ALL you need to know. If full specs are not available - walk.

Once you do this you will see that Sonnenschien gel, MK Gel, or Odyssey for sport or performance use are with very few mainstream exceptions - absolutely the only batteries worth buying. All the rest are quite simply JUNK.
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 21 May 2015, 20:13

Now for something completely different! I often tend to take the p**s out of Mark at the Junkie site. But this is one post that is absolutely correct that I just read. (About the only one however and a bit of this is wrong! And that's this part: They have a lot of rotational weight etc which actually has almost no affect on range at all). He just doesn't get physics... So ignore much of 1. Although flat free tyres ARE harder to push, for other reasons so give less range. So He is correct but for the wrong reasons. But read this:

Mary, because battery range is so subjective -- from your environment to pneumatic versus flat-free tires to the quality of the batteries to charging habits -- you can see huge variances. I can tell you that the Q6 Edge 2.0 and M300 get 15 miles, but that doesn't truly tell what you get.

Beyond your environment, there are two major factors that effect range.

1. Flat-free drive tires are great, but they decrease range by 20% on any Group-3 chair. They have a lot of rotational weight, so they require more energy to propel; they have a flatter profile, which increases rolling resistance; and, they're rarely truly round or they have flat spots. By contrast, pneumatic drive tires have far less rotational weight, so they require less energy; the tread crowns when inflated for less rolling resistance; and, they're round for less rolling resistance.

2. Over the past year, much of the industry has switched from quality batteries to very low-quality, ultra-low-cost Asian sourced batteries. If you use any of the major national providers, they've all switched from MK Gels to Asian "8-month" batteries that can dramatically reduce range. In independent lab testing, the "new industry-standard" batteries show good range for around 30 cycles, then plummet, where range tanks. For the average user, this means that your chair's range is dramatically diminished. By contrast, MK Gels start with great range and maintain it for, typically, 500 cycles. Great batteries are becoming hard to get, so demand quality and know what's in your battery box.

Therefore, for any user wishing to optimize range, pneumatic drive tires and quality batteries can maximize your Group-3 power chair's range by literal miles.

Lastly, if I could scream one thing to the complex rehab community, it's CHARGE YOUR CHAIR!
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 19 Jul 2015, 10:15

And I see several posts this week on the junkie site by mark, mentioning internal resistance of cheap batteries, giving less torque etc,

That's all new from him! And finally some sign of learning something about batteries. He must have been over here reading some of these posts... :lol: Shame we cant get him to understand chargers or charging...
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Re: HOW to choose a LEAD BATTERY

Postby Amnot » 31 Jul 2015, 17:23

To Burgerman:

I went to the Odyssey website and could find no reference to wheelchair batteries whatsoever. I know that you only made reference in your post to "sports" and "performance" Odyssey batteries, but I'm a bit fuzzy on how to translate from one use to the other. Could you add some detail on how I could select an Odyssey battery for my wheelchair?


To all readers: I wanted to clarify that my old batteries have a 75ah rating
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 31 Jul 2015, 18:50

Those 75Ah batteries, will not give you 50Ah if you use them at a high rate. And you will be lucky to get 35Ah out of them in real world use due to the voltage drop under load.

Don't fixate on Ah. A battery that starts out at 75Ah, but runs out of steam with 35Ah still in it but not USABLE, and so you stop anyway, is of zero use! That's what Peukert, and internal resistance do.

The closest Odyssey you will find is a Grp 34 PC1500 with 68Ah. But depending on HOW you use your chair, and how its programmed, they may well carry you further. So for severe use they are better. Faster charging, longer range, and able to give you more torque or climbing power for sport of off road use.

In a wheelchair we use short bursts of high amps. So we may spend hours sat about, or cruising along at full speed, but this is easy for batteries, it doesn't take many Amps. But turning on the spot, driving up ramps, off road, sport takes hundreds of Amps. It LOADS the batteries. If this is not you, buy MK gel. If it is buy PC1500 Odyssey.
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Re: HOW to choose a LEAD BATTERY

Postby ex-Gooserider » 04 Aug 2015, 04:55

A wheelchair is just another load, though a high demand one, so just because a battery does or doesn't say Wheelchair in it's advertising doesn't really mean much about how good it is...

Odyssey batteries are NOT the best choice for users that don't push their chairs hard, and the industry doesn't really want to admit that people like us that DO push hard exist, so Odyssey doesn't try to position as a powerchair battery supplier... However by giving up some cycle life, those of us with high demands get better performance....

OTOH there are other manufacturer's that make really crappy batteries that will (sort of) work in a power chair, so they list that as a possible use....

ex-Gooserider


Amnot wrote:To Burgerman:

I went to the Odyssey website and could find no reference to wheelchair batteries whatsoever. I know that you only made reference in your post to "sports" and "performance" Odyssey batteries, but I'm a bit fuzzy on how to translate from one use to the other. Could you add some detail on how I could select an Odyssey battery for my wheelchair?


To all readers: I wanted to clarify that my old batteries have a 75ah rating
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Re: HOW to choose a LEAD BATTERY

Postby Bearded_Blunder » 29 Nov 2015, 10:26

Any opinion on the Concode Battery products? (badged variously as Lifeline, Sun Xtender, and Chairman) the "Technical Manuals" for these all read the same so I suspect the only difference is dye in the plastics, termination, and labelling. Given the cycle life is quoted in the 550 range for 80% DoD, I found an internal resistance figure of 5mOhm somewhere (can't find it again, so can't be sure it's correct, but they boast a lot about low IR values), they would seem to be a reasonable alternative to MK or Sonnenschien Gels on paper, the new IR figure is close, but shouldn't degrade as much from mobility chargers set at AGM voltages creating voids, as they're AGM batteries, and would likely be more tolerant of fast charging too.

Of course I may be missing something obvious, hence asking, but they look a reasonable alternate to me by the specs, if my logic is correct they'd only be slightly worse than MKs new, but quite possibly better 3, 6, or 8 months later, which may be a reasonable compromise, they're ludicrously priced in the UK but then anything with "marine" or "disability" in the description always doubles the price, but possibly viable for American purchasers where they seem more on a par with other deep cycle batteries with regards to price?
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 29 Nov 2015, 11:20

Well they sound better than some at 7 or 9mOhm.
But when you consider that the PC1500 68Ah Odyssey (a group 34 so smaller and lighter) has 2.5mOhm IR, it puts the 5mOhm figure into perspective. It can deliver DOUBLE the Amps before voltage collapses.

It means that they will have double the voltage drop under load compare to the Odyssey. Remember that this resistance increases with discharge level too. Until the partly discharged battery will no longer drive your chair and you stop with about 1/3rd to 1/2 the Ah remaining but unusable.

So it related directly to range as well as torque.

But as you say the MK is 4mOhm, so not great, but not much better than these concorde batteries. So on the face of it it wouldnt seem that bad. But its still some 20 percent worse for concorde.

But then thats also why I dont use MKs... They will only let me pop wheelies when new, and when fully charged. After that the lights dim instead... That may only be a 20 percent change!

Would you notice a 20 percent power loss on your car? I certainly would.

If you load up your chair on a curb/or as I show below -- a tiny wheelie for eg, and pull the max Amps the controller allows, the battery voltage drops like a rock then instantly recovers. Thats resistance. If it drops below a certain level, (and it does) then the controller cuts back on power, to stay in control and to protect the battery. (You dont get your full 100A per motor...) It does this typically at around 18 volts give or take. So it can directly affect torque.

Watch this: http://www.wheelchairdriver.com/gopro/voltdrop.mp4

The big digits are "live" battery Volts. The three smaller ones below that, all start at the same figure before a tiny hop/wheelie, but read and keep the peak values. Like this:
Highest V. xx.xxx
Average V. xx.xxx
Lowest V. xx.xxx And just one tiny wheelie, drops the voltage here down to 18.9v, from a resting fully charged 25.x something... These are MKs.

Consider what happens by say 50 percent discharge when resistance has increased and voltage already fallen. It will drop way more still. And consider what happens as the battery ages... Worse, peukert level is related to IR too. So that value also will be worse on concorde. All this is why I use Odyssey.
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Re: HOW to choose a LEAD BATTERY

Postby Bearded_Blunder » 29 Nov 2015, 19:39

I fully comprehend the advantages of the Odessey batteries over these, however, I was leaving them aside for the purposes of this enquiry, there are some chairs they don't fit without modifying battery boxes, others have weedy 4mph chairs that don't see the full advantage of the Odesseys.

The main point of the enquiry was, for those who choose not to go the odessey route, is the point regarding possible slower degredation of performance compared to MKs possibly valid? I completely understand 20% worse when new, and of course my two relatives may well notice, though any new battery will be a marked improvement over the cheap agm batts curreently fitted and ailing.

The nub of the question is about some time later, after the typically misconfigured for GEL Mobility chargers have created voids in the electrolyte and increased the internal resistance, just wondered if anyone had any real world experience to show if this causes a crossover in performance later? Or do the MKs take so long to increase internal resistance by that 20% that both sets of batteries are knackered and need replacing anyway? Meaning no possible advantage.

I'm just trying to make the best informed decision I can, Odesseys would be wasted in my sister's chair, her usage is so light she has got several years from cheapo generic chinese AGMs fitted by the vendor just prior to her purchasing the chair used, when those fail, she'll likely opt for the same again.

My niece's chair use is considerably more, and due batteries soon owing to limited range and poor slope climbing, but it's still a weedy 4mph chair with a low amp controller, and I doubt the pride onboard charger is correctly configured for GEL batteries voltage wise in either case. But if you tell me from experience that MK or Sonnechien are still likely to outlast "half decent" AGMs, I'll bow to your superior experience.
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 29 Nov 2015, 20:10

The nub of the question is about some time later, after the typically misconfigured for GEL Mobility chargers have created voids in the electrolyte and increased the internal resistance, just wondered if anyone had any real world experience to show if this causes a crossover in performance later? Or do the MKs take so long to increase internal resistance by that 20% that both sets of batteries are knackered and need replacing anyway? Meaning no possible advantage.


There's a lot of variables. So I couldn't tell you. But my betting would be that on a lightly loaded chair there would be little difference in range, longevity in real terms. But on one programmed to go, higher speed, or hills, heavy user, then I would get the MKs.

And MK claim 550 cycles in some publications, 500 in others. Again it depends on temperatures, charging regime and algo, time period, discharge rates, etc too.

As for knackered and needing replacement then that too is subjective. I find 10 month old well cared for Odyssey or MK ready for replacement. No power! They feel tired and I lose wheelie or accurate turning ability. Feel like steering with an elastic band. With typical delayed programming you couldn't tell...
Yet a user with 7 year old badly cared for batteries in a weedy powered deckchair will tell you her batteries are just fine! And that I am mad. But on a real test they are beyond ruined, 3x the resistance, 1/4 the Ah they started out with. Yet she cant tell!
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Re: HOW to choose a LEAD BATTERY

Postby Bearded_Blunder » 30 Nov 2015, 00:22

What I actually need is a decent hobby charger, or to brew up some other way to determine the actual capacity of the niece's batts, I know they're knackered though,if I could measure it I'd have a number I could use to pronounce on the next set, I'm using a very simple method to determine knackered, namely if she forgets or doesn't get time to charge after the morning school run, is there enough juice for the afternoon one, with the present old and undersized batteries, that's borderline.. so she needs new and better.

Meantime I do have the gear to measure the charger output, which I plan to do, at least MK have some info about the effect on cycle life of charging regime, so once I know values I'll have a handle on how good or bad the charger in question is/would be for GEL batteries vs AGM. That will probably be the determinant on which I suggest she budgets for out of your three recommendations, if the charger is badly out for GEL, it'll be either Odesseys or the next best spec I can find in AGM.

Then save for a better charger while the chair is killing those, so MK becomes viable.
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 30 Nov 2015, 01:32

You CAN charge mk above the "best" 14.10V recommended for best cycle life. You just lose some cycles.

You also cannot simply measure capacity. I have a set of old MK batts here that are 7 or 8 years old. They measure 69Ah. On my hobby charger, down to 10.1v @ the 20 hour rate. That's just 4Ah down on new.

But they wont climb a ramp, and you get to go once around the park, before you grind to a halt. About 3 miles...

You need to take into account internal resistance, and peukert. And the point that the control system no longer works (around 18 volts under load) etc.

Anyway if it helps:

www.wheelchairdriver.com/MK1.pdf
www.wheelchairdriver.com/MK2.pdf
www.wheelchairdriver.com/MK3.pdf
www.wheelchairdriver.com/MK4.pdf
www.wheelchairdriver.com/odyssey.pdf
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Re: HOW to choose a LEAD BATTERY

Postby Bearded_Blunder » 01 Dec 2015, 07:40

Burgerman wrote:You also cannot simply measure capacity. I have a set of old MK batts here that are 7 or 8 years old. They measure 69Ah. On my hobby charger, down to 10.1v @ the 20 hour rate. That's just 4Ah down on new.

You can, though it probably calls for a homebrew discharge or bigger discharge tester rather than a typical hobby charger, because as you said the 20 hour rate yeilds no useful information being too slow to provoke much voltage collapse under load, the 5 hour rate will show a much greater capacity loss on a tired battery vs a good one though.

Given both 5 hr and 20 hr capacity measurements, it's possible to calculate Peukert, and predict the capacity at any other arbitrary load. That's too much sums for simple pass fail decisions, but capacity loss compared to new at the 5hr rate should be indicative, sufficient for rule of thumb decisions about if a battery is past it for traction use, but still great for solar lighting in the shed. Marked loss at the 20hr rate would indicate it's toast for either purpose and useful only for recycling or doorstops.

Deep cycle batteries (flooded) were my light, entertainment, and running water for over 10 years continuous off grid caravan living, I'm not quite a complete novice with them, even if intermittent high load situations were atypical, the specs for half decent ones like Trojan (not the leisure rubbish at Halfords/camping shops) make those look almost viable for chair use, they ought to outlive and outperform the cheap chinese AGMs on offer from mobility shops at about the same price, they just take more care and feeding than I'm interested in doing, and a better ventilated charging station than is convenient.

I'd never recommend them to anyone for a powerchair, because of the safety and mainenance issues, but if finances were sufficiently tight, I might pick them myself over cheap AGMs to keep the girls rolling, since I'm fully aware of (and was very used to) the extra risks and work I'd be getting, I'd rather not unless forced though, pulling seats and shrouds off regularly for electrolyte checks is a really unappealing idea.
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Re: HOW to choose a LEAD BATTERY

Postby rowallen » 03 Dec 2015, 12:32

A couple of major scooter manufacturers have recently been telling customers that MK batteries are not as good as they used to be, and have been selling them other types. Is there any truth in this or is it just a line to push batteries with a better profit margin?
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 03 Dec 2015, 13:20

They are exactly the same. And the same specs as ever. But they are expensive. Those, Sonnenschein A500 dryfit, or for sport/heavy usage and for faster charging, Odyssey PC1500 are the only ones worth fitting.
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Re: HOW to choose a LEAD BATTERY

Postby rowallen » 03 Dec 2015, 13:48

Thanks Burgerman.
My current MKs are over five years old and are still holding up, distance-wise and on steep slopes. I'll probably renew next year anyway but don't mind paying for a good product.
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 03 Dec 2015, 14:29

A question.

How do you know?

Every time someone tells me they have good batteries that are 5 year old, they really mean that the batteries don't impact their daily routine.

That doesn't actually tell us much. In about 50% of cases if I actually test them, as I do with friends and chair users I know locally, they turn out to be absolutely wrecked! But the users don't use them hard enough or go far enough to tell. In the other cases they may well still be 80% as good as new. It all depends on how they are looked after, how deeply discharged, how they are charged etc.

In all these cases, measuring volt drop under load when new, and when old will help diagnose. Likewise a cycle down to 10.8V over 20 hours will allow a hobby charger to tell you how many Ah they can still provide.

Of course the time to change them is when it starts to impact your life.
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Re: HOW to choose a LEAD BATTERY

Postby rowallen » 03 Dec 2015, 15:19

In answer to your question, I guess I don't really know.

I'm currently judging them by how they perform under my main usage which is pootling around the New Forest at 4mph and climbing the odd steep hill or bank. So if I can do 10 miles of track and offroad and still have a couple of bars left then that's good enough. Last month, I did a 50m 1-in-4 on tarmac at the end of a day out and it was slow but OK. However, I'll bet that if you put my batteries into your powerchair you'd be horrified.

I've recently been investigating improving the performance but have ended up copping out with an "if it ain't broke.." approach (mainly for budget reasons).
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 03 Dec 2015, 16:56

Well if it works for what you need, no need to fix it. As long as you are aware so that if you get caught out and need to do more it doesn't come as a shock!
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Re: HOW to choose a LEAD BATTERY

Postby Scollard » 05 Dec 2015, 02:03

Question BM,

I'm building a Lithium pack to replace my lead batteries in my Pride Pursuit XL mobility scooter.. I have an interesting development with my lead batteries (group 27, 100 AH). When I installed them initially I put them on a car charger and charged them individually overnight and let them float for a while to make sure they had a fully saturated charge. I then wired it all up and everything was fine. Unfortunately I didn't have my hyperion charger, it was at my other home 2000 miles away, so I couldn't do a discharge test on each battery. Now I have one battery that is running about 71 AH and the 2nd battery is only 1 AH. I have to think that the 1 AH battery must have been faulty to begin with. What do you think? I followed good battery tending. I charged overnight every time I used the scooter and at least once a week overnight if it wasn't being used. It sits in my garage and the temp rarely falls below 10C. What would cause a battery to crash that badly other that if it was faulty to begin with? It seems strange that one battery is still good and the other one is fried and they have been treated identically.

J.
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 05 Dec 2015, 02:06

Failed strap internally or something. But 1Ah? The chair would not move.
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Re: HOW to choose a LEAD BATTERY

Postby Scollard » 05 Dec 2015, 02:40

It doesn't really move. I can go to the end of the driveway to pick up the mail as long as I move along slowly. When I get back the gauge has drained all the green lights and is in the yellow. My Lithium pack will fix all.
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 05 Dec 2015, 11:40

Well its either failed where the plates are attached internally, or you have a bad cell, that was caused by impurities or physical damage to the plates. And its now high resistance.
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Re: HOW to choose a LEAD BATTERY

Postby terry2 » 21 Mar 2017, 15:44

I've found out after getting 8mph motors that my MK gel don't last very long at top speed :(
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Re: HOW to choose a LEAD BATTERY

Postby Burgerman » 21 Mar 2017, 15:58

Theres a few reasons you get less performance, range, and service life with 8mph motors.

They draw about 25% more Amps, on every manoever, turn, ramp, hill, at every speed including indoors. Because they are geared taller. You load the motor more all of the time.

And when traveling at a higher speed you draw more Amps. That wouldn't matter because you also get there quicker so range should be almost unchanged.
But... Batteries, esp gel batteries, suffer heavily from peukerts law. Which states that with lead batteries (only) you get less actual usable Ah out, the faster you discharge them. So going faster empties them faster because you HAVE less Ah available.

Fun no?

That is why I like brushlesss gearless motors. They take you 40% to 70% further per charge at any speed. E.G my new chair has a ISO range of 38 miles instead of 20...
And lithium, takes you twice as far, or more on top...
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