MK gel batteries 15 years

[Raro]

How many years do your batteries last? In 2023 I changed the MK 73ah batteries for the first time in my chair purchased in 2008..

[Burgerman]

That depends.
How do you determin when they needed to be swapped?

MK gel, when charged CORRECTLY which mobility chargers do not do, can do 500 cycles (discharge, recharge) before the original capacity is 20% less than it was in the start. At this point they are considered end of life. This is true if you discharge them to a level where 20% remains daily. So 80% discharged. On top of this, even if kept in standby use for say a generator or UPS, they have a 10 year calender life. After this point they are also at end of life even if never discharged. So these two things both kill them off.

Now if you barely use a powerchair and you charge it properly and very regularly, you will both get many more cycles than 500, and will not be aware that they are long past the end of life anyway. Because you dont go far enough to let it affect you. If you discharge the batteries almost fully every day you will get around 100 to 150 cycles before they die. So 4 months. If you barely use them, you may get 2 or 3 years. 1000 cycles. You cannot realistically get more, you just dont know they are knackered!

I MEASURE the capacity using my hobby chargers. So I KNOW what Ah they can still give.

How long do mine last?
I also used to replace MK gel batteries every 9 months to 10 months when the range began to affect me. When I measured them this was when the Ah capacity had fallen by approx 10%. So to me, they were end if useful life. I then gave them to some old ladies in an old folks home that is at the rear of my house. They continued to "use" them for at least another 5 or 6 years. So again, what do you consider end of life?

Here is MKs own cycle life V capacity graph. Page 3
https://www.wheelchairdriver.com/MK0.pdf

I suspect that if I had actually tested and measured your batteries after say 2 years they would have already deteriorated to the point that they had lost 20% of their original capacity and be considered end of life.

Heres how I measure ACTUAL capacity with the hobby charger PL8 accurately below:

Below is an AGM battery. It was rated at 80Ah and when discharged at the 20 hour rate it gave me a measure 74Ah (74,000mAh see screenshot) when discharged to the specified 10.8V or 1.8V per cell.
So it has lost around 6Ah. Thats about 8% of its rated capacity lost. So officially about halfway through its service life. About 8 months old.

[Burgerman]

A more interesting question might be how long do your motors last. Because I generally swap them after 2 years use because from experience across many makes of chair an motor know that they fail and let me down soon after this. Again this isnt a thing that happens to most people. Because I have my chairs programmed to respond. And when my dog was alive I went at least 5 or 6 miles across grass and feilds, parks etc daily. Before going into town to shop/bank/eat. And then to the pub every night. And that sort of heavy use means motors and batteries fail fast.

Heres a picture of a few motors that died... In a 7 year period.



And loads of trashed motor brushes like these on my bed...



And endless cush drive motor couplings...



The reason I ask, is that if you are NOT doing this to your motors, gearboxes, and tyres every few years, then your batteries are going to be getting a far easier life than mine do. So realistically you will get at least 2 years maybe three.

I no longer do this either. Because I got older, and calmed down a bit! And because no dog. And I go places sometimes without wheelies, or curb jumping...

[Raro]

During the time that this chair has been used, I cannot tell you the kilometers because it does not indicate it, the batteries have never been charged correctly, at least my method was to charge only when the charge indicator is halfway, until they completely died I could travel 18 km on a charge, but everyone I know complains that once the original batteries have been changed, the new ones last a couple of years at most.

The motors and the rest of the chair have never had a problem. The use it has had has always been on the road as much as possible. The terrain is quite flat and I weigh little.

[thamesmud]

A more interesting question might be how long do your motors last...

Wheelchair torturers hell-scape pictures shock internet !

[martin007]

How many years do your batteries last? In 2023 I changed the MK 73ah batteries for the first time in my chair purchased in 2008..

15 years!
Does that chair come out your room?

[Raro]

It has never been inside the house, it is a Groove R and it has never gone slowly, always at full speed.

[martin007]

The powerchair never come into the house?

[Raro]

never that chair only in the garage

[martin007]

Any user with a minimum of experience can tell you that the only way for a battery to last 15 years is to use them very little.

[Raro]

During the winter I didn't use it but the other months I did. In my opinion, even if you don't use the chairs, it doesn't mean that the batteries won't run out. I highly doubt that others will last the same for me.

[Burgerman]

Even if completely unused they dont actually last 15 years - even if kept on a temperature compensated permanant float voltage. It will have lost more than 20% of rated Ah capacity at 10 years, best possible case treated with perfect laboritory care.

Whats actually happening here is that he is confusing "still works" with still healthy. And that isnt actually possible. Odyssey too, another good quality battery that can be deep cycled etc at great cost has the same 10 year calender life limit too. And almost the same cycle life.

If I actually measured its internal resistance it will be at least double that of a new battery. If I measured the capacity it will be down by over a third. Especially at a high rate like the 2 or 3 hour rate we need.

Since it hasnt been actually measured all we have is seat of pants measurements which do not tell us anything very useful.


In any case. It doesent really matter. Because the time to swap out a battery is when you notice that it impacts on your usage. When it starts to affect your day. That may be after a few months when its dropped by say 8 to 10Ah. Or a few years for an average user. Or 15 years if its kept charged and you do not ever go far enough to know its only holding half what it should!

[Burgerman]

In my opinion, even if you don't use the chairs, it doesn't mean that the batteries won't run out. I highly doubt that others will last the same for me.

A n unused battery dies because they self discharge and that allows them to become sulfated. So you must keep them 100% full. Batteries age regardless to a degree. Even if not used. But you can slow it. the best way to preserve them is to store them DISCONNECTED from any drain. That means your chair because even if turned off it still pulls a few mA from the battery all the time. And if you do that, and give an overnight charge every 2 weeks to every 4 weeks without fail. OR store them connected to a float charger that has its float output at 13.35V x2 not more, they will last with the least possible / slowest deterioration. This is the 10 year float life that some quality batteries are capable of.

Also COLD is better for storage of all kinds of batteries. Cold slows down the chemical reactions that make a battery work, and the ones that gradually destroy it over time. So warm batteries give better performance. Cold ones live a lot longer. So cold for storage. This applies to almost all battery types. I keep all my hobby batteries at 2C in the fridge.

DEEP CYCLING batteries (going a long way) kills them massively quicker! Can be as litte as a few months. So always fit the biggest battery possible so that average depth of discharge is less. And the best possible quality.

Theres literally 4 only that I know of that can stand up to powerchair usage. MK Gel. (NOT MK AGM!). HAZE GEL, The ODYSSEY battery, and the new one that Permobil sell. And no it doesent need their fancy charger. Thats marketing nonsense. But ALL these 4 batteries MUST be charged and treated correctly. Theres no mobility chargers that will do this that I eer saw.

[Raro]

I'm not saying that they were in optimal condition for me, that they take a load and help me get from point A to point B. Obviously, it doesn't run the same completely full as it does with a quarter or a half full, I did 18 km with a load before they died. completely. It is usually very cold here in winter but the garage does not go below 10°, only the chair charger is used.

[Burgerman]

Well batteries improve over the first 10 or so cycles. Then after the first month they start a slow annd steady decline in capacity with every charge. They should never just suddenly stop working. Just get less and less useful over time/cycles. Until they hold almost no charge at all. And during this long slow decline the ability to make high currents also deteriorates as internal resistance also increases too, so steering and ability to make good torque starts to get worse.

The difficulty is in deciding at what point this should mean that you replace them. Theres no fixed point. Its really about cost and at what point it begins to interfere with your usage. The manufacturers quote a end of life at the point where 20% loss of capacity occurs. To me thats way too late as it leaves me unable to go about my normal day at least in summer. So I used to swap them sooner. To someone that never goes far, sits at home most of the time then they may never find a problem until half of the capacity has been lost. So they were never aware that the battery was well beyond any normal service life. And they then consider that their battery is still good many years after it has actually turned into a boat anchor.

[HiltonP]

Any user with a minimum of experience can tell you that the only way for a battery to last 15 years is to use them very little.

It's not quite as simple as that.

My first set of MK batteries lasted me over 20 years.

During that entire time I used my power chair everyday, for at least 12 hours at a time, sometimes up to 16 or 18 hours per day. The difference is that most of the time I was covering hard surfaces (wood/tile flooring indoors, and brick/cement paving outdoors). In addition to this I am extremely lightweight, and therefore not placing any real stress on the wheelchair. Added to this was the fact that chair was kept in a warm, dry environment and well maintained.

When you combine all of these factors you can get long life out of your batteries.

[Burgerman]

My first set of MK batteries lasted me over 20 years.

They may have "lasted" 20 years. They were end of useful service life long long before that!

They are, according to the manufacturer at end of useful life, and down in capacity by 20% after 10 years float life when used as a backup battery. Thats as long as they can last. In float use. And down by 20% would be very noticible to many users inc me.

As far as cycle life goes, MK state that after 500 cycles they are again down to 80% of original capacity or range. And internal resistance increase means you will not then still have 80% of original range. Maybe 60 to 70% depending on chair/load.

So no way on earth that a 20 year old battery - even if charged CORRECTLY which they seldom are, certainly not with a mobility charger - is anything other than a doorstop for at least 15 of those years.

Will it "work"? That depends on you definition of work. Probably still hold some sort of charge after 3 years. But completely useless. They never stop "working" as such. Just get ever smaller, ever less able to make high currents.

Added to this, a warm enviroment speeds up capacity loss. Cold makes batteries last longer.

[Raro]

They never stop "working" as such.
.

Yes, they stop "working" they do not take charge, the voltage drops below the working range or even remains at zero and there are batteries that do not last at all. I am not an expert but there is no battery that lasts as long as the original ones.
It also happens with cars, why?

[Burgerman]

The battery is allowed to have its voltage fall below that of which the charger you have from charging it. That doesent mean that the battery stops being able to be charged. It just means that YOUR charger can no longer charge it because its voltage has dropped too low. This can happen even with a new battery.

The more sulfated the battery gets from NOT BEING FULLY CHARGED the faster its self discharge level is. So they go dead if left unnatended more quickly. And they have reduced capacity. So KEEP THEM CHARGED at the correct float voltage for long service life. Any battery sat unused at any state of charge other than 100% is gradually dying and suffering permanant damage.

If you then connect another battery to it for a while, and then try again it will charge. The battery will always take a charge, no matter how small. Theres nothing in there that "stops working" suddenly. They just deteriorate day by day. This can be rapid or slow depending on exactly what you do to it and how its treated.

Older batteries are and were no different to todays batteries. How do I know? Because I actually MEASURE them Scientifically. I have done this for 45 years. I used to sell batteries. I also learned a lot about them. They do just as many cycles as they always did. They all measure the same internal resistance (as AC impedance) as they always did. They have the same calendar life that they always have had. Each decent brand of battery is very carefully made, to a certain spec and very carefully measured and tested to match a lot of legal standards.

Its true that there are now many cheap brands mostly made in china that are absolutely junk even from day 1.

Its also true that powerchairs have over the years become much heavier, with weights going from below 100kg up to 185 to 190kg in a modern chair. That means double the average daily discharge level when going the same distance. That literally means 1/4 of the sevice life from your battery alone! As the deeper the discharge the massively faster the battery active plate material is "used up". Then we have faster chairs. Faster chairs also draw much more current from the battery even when traveling slowly. And especially so when turning or climbing a ramp. All of these things mean that the typical 70Ah battery is now way undersized for the job. It is tortured in a modern chair.

Same thing is happening with cars. Modern cars have a mass of things that draw power from the battery all of the time while parked. The engine management system and keyless entry, radio key code maintainance, remote start, alarm and imobiliser systems, and much more mean the battery is always in a less than 100% state of charge even 10 mins after you stop. This allows it to sulfate internally over time. Which murders the battery! So the battery dies much faster due to sulfation.

The battery itself, is unchanged. Its what we do to them. And what we DONT do to help them out, that kills them off.

[Raro]

Call it what you prefer, batteries, like everything in this life, break, no matter what you want, there comes a point when they are useless and being the same brand and manufacturer, not all of them last the same.

[LROBBINS]

In about 40 years I have actually had two sudden lead battery failures because of shorted cells, so it can happen, but is pretty rare.

[Burgerman]

I used to sell batteries. The shorted cell thing are generally starter batteries. Cranking currents causes localised heat and warps the plates. Sulfation from undercharing can also warp them. I never had a battery that wouldnt hold any sort of a charge. Or that failed totally. Except one. Even ones with a shorted cell. Which can happen to old or fresh ones by the way. True they are still useless. Just like old ones knackered sulfated ones are. When I got batteries back under warranty, I always cut them open to see what gives. After a capacity test and load test and resistance test. If I send healthy batteries back I dont get a refund. Likewise if killed through ignorance. Almost non are manufacturing faults.

The only one I ever had one after selling warehouses full of the things over a decade that really failed like an on off switch. It was an early AGM "traction" battery by Haze around 18 years ago. It was MINE. A year old, getting tired and it cut off all power. Again, the chair would turn on. But not move. I was crossing a road quite normally with a full charge. I had to be rescued. That one when cut open, was a manufacturers bad weld between cells. The lead strap which was supposed to be a lead "weld" joining cells was badly made and had come apart.That is a freak failure. So that type of failure is more than 1 in a thousand. It just realistically doesent normally happen.

When a customer returned as "wont charge" or failed, or dead, wont hold a charge etc I always tested them. And not a single one couldnt be charged at all. In some cases they were almost as good as new. In others maybe 2Ah remaining capacity at best, and a charge never completes, from a 100Ah battery. But thats still a charge of sorts. Even shorted cell batteries can do bettter than that.

Mostly they had been left without adequate charge or been allowed to discharge and were all rammed full of white lead sulfate. Probabbly 90% of the failed ones. And in some cases they were "dry" and had been overcharged. Electrolyte long gone! In most cases with starter batteries its a combinaton of shorted cells that go too high resistance, plate corrosion, plate distortion that causes them to short out, due to sulfation and a lot of unwanted reactions from impurities reacting and doing god knows what. Mostly on deep cycle batteries though its because of undercharging. Non of that other than some odd reactions caused by impurities is a warranty claim. Batteries dont die they are killed in 99% of cases by ignorance and crap chargers.

A healthy battery when cut open is black on one plate and grey/blue on the other with no white deposits and clear correct level electrolyte with no plate distortion.

[HiltonP]

My first set of MK batteries lasted me over 20 years.

They may have "lasted" 20 years. They were end of useful service life long long before that!

They are, according to the manufacturer at end of useful life, and down in capacity by 20% after 10 years float life when used as a backup battery. Thats as long as they can last. In float use. And down by 20% would be very noticible to many users inc me.

So no way on earth that a 20 year old battery - even if charged CORRECTLY which they seldom are, certainly not with a mobility charger - is anything other than a doorstop for at least 15 of those years.

Well, for supposedly "useless" batteries they certainly were able to put up a very good performance.

Way after 15 years of constant daily usage I was still able to load up my powerchair with a picnic basket and DSLR camera bag and head up into our local Kirstenbosch Botanical Gardens (which are anything but level) and spend the day touring the gardens and exhibition halls.

Doorstop..... Not quite.....

[Burgerman]

If you dont go far enough to tell then obviously then you cant know. The thing you didnt do was measure them. Just bcause it was adequate for that trip doesenrt mean they are even close to healthy. You would find that you probably only used 10 or 15Ah. And that they now only held 25... Thats typical for a set of decade old batteries.

Because after 500 cycles (charges) then they will be down by 20% approx. And used daily thats only around 14 months. After 10 months the lack of range already affected me. I have to start topping up before going out in an evening. Thats under a year! You cannot be using the chair in the same way that many of us do. These are MKs own figures. Have a read. http://www.wheelchairdriver.com/MK0.pdf as its very educational.

If you have a chair that is programmed to respond as mine do its not only the capacity that is a problem (for me as I use at least 40Ah before I go out again in an evening) then the problem becomes a new one. It doesent respond properly. It "feels" like a set of dead batteries - gutless, incapable of wheelies or curbs etc. Or responding to to the level of turn response I expect. If your chair isnt programmed this way then you cannot feel this either.

[martin007]

It is obvious that there are people who barely use their powerchair...

[Burgerman]

Thats why I give my old knackered batteries to the care home. They dont know the difference and use them for another 5 or 6 years. For their uses they work fine. But for me they are useless.

The time it is "financially" sensible to swap a battery is when it affects you. But dont be under any illusion that a decde old battery is healthy. Even if its seldom been used. They calendar age as well as wear out due to discharge/recharge cycles. And that limit is both 500 cycles and 10 years float use. Both time and use gradually destroy them starting at about 1 month old and they get worse every day. In my case fter 9 monhs I can feel the lack of performance and I cat see the range is inadequate for my day. They also deteriorate faster if its warm or if charged badly (hello mobility chargers!) or not often enough. Or for long enough.

It would really pay EVERYONE to read this page by MK. This applies to all gel batteries. Not just MK. And after you read it realise that all the mobility chargers charge well above 14.1V and they do so for an inadequate time! Over volts and undercharged. The undercharging causes further damage (sulfation) which speeds up the damage caused by the too high voltage even further!

http://www.wheelchairdriver.com/MK0.pdf

[Raro]

The time it makes "financial" sense to change a battery is when it affects you

we agree

Out of curiosity, how many kilometers can you do on a normal day? Are you still using gel batteries? How many charging cycles will the batteries last in optimal conditions, charging them correctly for 300 cycles according to the graph?

I would encourage you to post a post telling what is the correct way to charge the batteries and what to use to do so.

[Burgerman]

Out of curiosity, how many kilometers can you do on a normal day?

I used to do around 15miles (23km) on average when I had a german shephard dog. But average in summer. Less distance in winter. That was because I topped up halfway through the day. Because realistically a set of lead batteries isnt capable of doing this. But its not about miles. The state of charge of a battery depends on load. And load varies depending on a great number of things.

For e.g it takes 100 battery amps to turn in place in a rear drive powerchair. It only takes around 10A to 15A to roll at full speed.
So that if I spend 1 hour at home with a leaf blower clearing leaves in my driveway, garden I could use up a full charge. And covered maybe half a mile...
Same indoors vacuum cleaning for e.g. That left/right repeated movement uses 6x as much power! And you go nowhere.
So its not about "range" or distance. Its about load.
What else determines load? Tyre type and pressures. Solid "flat free" tyres have higher rollig resistance compared to normally inflated pneumatic tyres. But most of my chairs have larger tyres which are inflated to low pressures to give a smoother ride. That means that it doesent set off my muscle spasm and cause tension and problems as I roll over our terrible pavements. What else causes high loads? User weight. CG position. Carpets or grass. Hills. And extreme loads are caused by a lateral slope used to help roads drain that slope left/right or right left. All these things can reduce a chairs range from say the claimed 20 miles to 3 or 5 instead. And temperature... Colder days = less range. So as I said, theres no such thing as how many miles or kilometers range you can do. The answer is it depends on many things.

Are you still using gel batteries? How many charging cycles will the batteries last in optimal conditions, charging them correctly for 300 cycles according to the graph?

I have 6 powerchairs. I have lithium batteries in 3 of these going back 15 years now!
I have ODYSSEY AGM lead batteries in a couple. Because gel batteries cannot provide the current or torque that my programming demands from them. These are much lower impedance, meaning they charge faster, perform better. Most normal people wouldnt detect the difference. But I only use lead in 3 of my 6 chairs. I have one with a set of gel batteries (these are 80Ah gels, so are charged the same way as the MKs, and the SAME SPEC as MK but slightly arger capacity but are in fact HAZE GEL 80Ah.

I would encourage you to post a post telling what is the correct way to charge the batteries and what to use to do so.

Approximately 1/5th of all the posts on this forum going back decades do exactly this!
Again only yesterday...
https://www.wheelchairdriver.com/board/ ... =2&t=12249


Theres no easy one size fits all answer.
I use my 4 bench power supplies to do a top up during the day to inrease range, and to make the battery last a lot lot longer. Set to 14.7V (29.4V) and 40A for AGM batteries. And set to 25A to 40A and 14.1V (28.8V) for gel batteries. This needs an anderson connector. If charging via the XLR port (I dont generally as its too slow) the same voltage but 12A maximum! You can use a mobility charger for that.

For a full overnight charge I use a 10A modified mobility charger to give me 28.8V and 27.0V float via XLR for gel. And an unmodified one for AGM. But these are crap.

I normally use the 3 stage charger from Shirley programmed to give me the same 28.2V (gel) and 29.4V (AGM) and set to stop CV stage at 0.2A and go to a 27V float. At 25A Gel, at 50A AGM.

I also frequiently use the same ZXD power supply to run the PL8 charger to charge Gel properly, same settings 25 to 40A or 12A via XLR port but with 8 hour CV limit, and no float. I use the same charger to discharge ad test and measure the battery capacity to determine its condition periodically too.

How many charging cycles will the batteries last in optimal conditions, charging them correctly for 300 cycles according to the graph?

Not sure I undertand that question.

[Raro]

About 1/5 of all posts on this forum from decades ago do exactly this! There is no single, simple answer that works for everyone.

That's why I suggested it because there are many long posts about it, I just wanted something shorter like what you just wrote, anyway I've already been reading the post that is posted above, I didn't realize it from the title.

[Burgerman]

Short version.
Charge every night. Charge in the middle of a day for an hour.

Anything can charge a battery. No matter how far away from what it really needs as long as it puts a few electrons back. Thats basically what a one size fits all mobility charger does. If you want to do better than that then you need to read the posts on here. And read the MK data. This will allow you to double or quadruple the service life. Knowledge is power and there is no simple dumbed down answer. No 3 line advice. The subject has a lot of ifs and buts and tech details.

For e.g here is the correct charge also, and variations inc fast finishing that MK specify:
www.wheelchairdriver.com/MK1.pdf

Also read this end to end, you will learn a lot.
www.wheelchairdriver.com/MK0.pdf

And this one shows you the differences beween the MK Gel and the MK AGM batteries.
www.wheelchairdriver.com/MK2.pdf

And this one is good info on the best battery ever made, the Odyssey lead batteries. These are ultra low impedance AGM. And pure lead. So not cheap. They can start a truck in siberia when half charged. They work as the highest CCA and CA starting batteries available AND can be deep cycled too. And in real day to day use they last as long as Gel batteries provided you get 100% plus a bit extra back into them every cycle. At a higher voltage than gel.
www.wheelchairdriver.com/odyssey.pdf