Gel vs Lithium Batteries

[wes4dbt]

Been just killing my U1 Gel batteries, only lasting @ 6 months. And I only use my chair @ 2hrs a day for shopping and taking care of business. Had a feeling the chair was to big for U1's. I now need to start using the chair around the house also so I just put a set of MK 40Ah batteries in it, that's the biggest that fit.

I really like the chair so if the MK 40's don't last I was thinking of trying these lithiums
https://www.walmart.com/ip/ExpertPow...E&gclsrc=aw.ds

They are the same size as the 40's but x2+ the money. Do they really get the number of cycles they advertise and would it be safe to use them in my chair???

Thanks

[expresso]

that link is dead - but i dont think any lithiums that walmarts carry would be a good choice -


can you find a working link to see the item ?

[Burgerman]

Correct.

They are the same size as the 40's but x2+ the money. Do they really get the number of cycles they advertise and would it be safe to use them in my chair???

Its highly unlikely that the built in BMS will allow the amount of current your chair demands on ramps, or zero speed turns etc. So it probably will keep cutting out. Esp when you have used some of the power. The only way to get good cycle life from lithium with a built in BMS and dumb charger is luck. And light use. They dont like big currents, or being discharged deeply or being full... They especially dont like being even a tiny bit over voltage or under voltage. Using a tiny pack with a dumb charger and built in BMS garantees that you will do all of the above!

So it might work. If it doesent keep cutting out when you need it most. That depends on specific BMS inside the battery. And it might work OK at least as good as the lead plus a little extra range. The real problem is that you are expecting too much from the chairs small battery.

If its cheap enough that you dont care if its problematic then try it. Whats the chair? And whats the battery specs? Because otherwise who knows!

[wes4dbt]

Thanks for the replies, here is the link

https://www.walmart.com/ip/ExpertPower- ... lsrc=aw.ds

[wes4dbt]

The chair is a Pride Air2

The current batteries are MK 40 ah Gel M40-12-SLD-G

https://www.mkbattery.com/application/f ... -SLD-G.pdf

[expresso]

i know its very tempting - but it may give you issues or may not - depends on your chair also

discharge is only 50a for this battery - if your chair pulls more than that - it may cut off - and the cost you need two of them

so will cost you about the same as making your own - minus the charge and PSU needed - but the battery itself - you may find a nice 120 ah or 150ah cells that may fit - same cost -

but i understand - i was the same way at first - i really wanted a drop in - easy - but glad i made my own - i need alot of battery -

nothing less than 150ah - 200ah cant fit - in my chairs now - so i go for the 200ah - in your chair - you need to figure out the space you have

what chair is this ?

[wes4dbt]

Thanks for the reply,
I couldn't find out how much current my chair draws in any of the manuals. As for how much room I got, well that's easy, it's the exact area of these new 40ah batteries. They fit snug, one on each side of the chair. But the thought of building my own power packs seems a little out of my league. Then again I haven't researched the subject.

I realize the best thing to do is get a chair with batteries that have a much larger capacity. But that's expensive, was hoping a $800 set of batteries might solve my problem.

[expresso]

those wont do much for you over lead - its only 50ah - thats about what you get with lead - not worth it - they may last more than a few years maybe - but your wasting your money with that

i know it seems hard to do your own - i felt the same - before i reached the point where i gave myself no choice - i did it with alot of help from here -

best thing i did - now in your case -- i dont know what size will fit - but i bet you can find some 120ah to fit in your space

now that will give you alot more range and last a very long time - using only 8 cells - its not hard at all - when i did it first time

we were using headway cells - was much more involved - now only 8 Cells - its nothing compared to 6 years ago - price is great size and Cap. more than 3x - 5x over lead -

the $800 you spend there - is about the same you spend on your own cells - then its wiring - charger and PSU - but those are one time items at first mostly - your choice - just think about it

[Burgerman]

Max. Continue Discharge Current: 50A

Again what chair is it? Because this is too low for any normal powerchair.

[terry2]

Thanks for the replies, here is the link

https://www.walmart.com/ip/ExpertPower- ... lsrc=aw.ds

"ExpertPower 12V 100Ah LiFePO4 Battery Tear Down!"

https://www.youtube.com/watch?v=8UJYm4g ... WillProwse

[wes4dbt]

Again what chair is it? Because this is too low for any normal powerchair.

I answered that a couple of post back. It's a "Air 2" by Pride Mobility, the full name would be Jazzy Air 2.

those wont do much for you over lead - its only 50ah - thats about what you get with lead - not worth it - they may last more than a few years maybe - but your wasting your money with that

50ah would probably be enough ah, I've been using U1 32ah Gels and they're find for about six months. I probably only get about 200 cycles. Then they start draining quickly, maybe a mile at most. What caught my eye was the number of cycles the Lithium batteries claim.

[wes4dbt]

Just watched the battery tear down video. Thanks, it was interesting but a little beyond my understanding. Didn't understand why he wanted it not to charge at low temps. Sure there's a reason. Can't believe he cut open a $700+ battery. lol

[Burgerman]

If he had any clue he wouldnt have bought it to begin with. And if you want it to last you need to dump the useless BMS to begin with. The cells are fine. Just need charging properly. That battery is a waste of time though because its group 27 size, so too big physically for a normal powerchair. And even then it is like all these direct lead brick drop in replacements LOW CAPACITY. Its possible today if you do it correctly to fit 8x 200Ah cells in the space of a smaller GRP 24 battery. So giving around double the capacity and range. Which extends calender life too. And at the same price. And no BMS needed (or wanted) if a proper cell balancing charger is used with adequate Ah capacity.

Why would he dismantle it? Because all these "experts" on you tube earn much more that the cost of a battery by posting all their "expert" garbage. The reason that you shouldnt try to charge a lithium battery at such low temps is because it ruins them.

Your chair uses a 70A PG VR2 power module. Thats 70A max per side (each motor). That batt is only capable of 50A total. It can do more for a bit, but thats typically not enough. The chair *can* take 140A (peak amps) from its battery when climbing a curb or ramp. The BMS will cut out to protect the small capacity 1C cells. So you stop till it is reset. So will it work? Maybe if you are gentle and dont stress it with high demand on ramps/curbs/threshholds or zero speed turns.

As I say with a small capacity lithium battery and a built in BMS its all a matter of luck. As is its reliability.

[Burgerman]

And:

When charging at above-freezing temperatures, the lithium ions inside the battery are soaked up as in a sponge by the porous graphite that makes up the anode, the negative terminal of the battery. Below freezing, however, the lithium ions aren’t efficiently captured by the anode. Instead, many lithium ions coat the surface of the anode, a process called lithium plating, which means there’s less lithium available to cause the flow of electricity and the battery’s capacity drops. Charging below 0°C at an inappropriate charge rate, also causes the battery to become less mechanically stable and more prone to sudden failure.

The damage to the battery when charging at colder temperatures is proportional to the charging rate. Charging at a much slower rate can reduce the damage, but this is rarely a practical solution. In most cases, if a lithium-ion battery is charged below freezing even once, it will be permanently damaged and must be safely discarded or recycled.

Non of which aplies to us charging indoors. So I usually charge at 35 to 40 Amps. So as to get a lot of power back fast. That sort charge rate doesent really apply to a small battery in your chair though. It is a very light indoor type or at best shopping chair with low power and small battery space.

[wes4dbt]

Thanks for the explanation, not what I wanted to here but that's ok. I'm curious how you found out my chair can draw 70a per side.

Let me ask, if I found a Lithium battery with a 70a discard rate, that fit my battery space, would I be able to just drop them in and go??? Would it require a different charger? From what you guys have said it doesn't sound like a simple swap out is possible.

I'm not ready to tackle building my own setup yet, just put these MK 40's in, so I got a while to think about it. I would be interested if you know of a good tutorial for a beginner like me.

Been interesting talking to you guys, Thanks again.

[expresso]

since the lead is new now in your chair - its a good time now to learn the lithium way - by the time you read and get yourself ready for making it yourself - you would need new lead - if you wait too long you will need new lead again and more money wasted on lead that wont last - now you have the time to sort it all out and consider making one for when the leads dies again

[Burgerman]

Thanks for the explanation, not what I wanted to here but that's ok. I'm curious how you found out my chair can draw 70a per side.

I looked at the chairs specification. It uses a PG Drives controller. Its max capability is 70A. per side. That means it can pull a maximum of 140A from the battery at times of maximum demand. Its limited to this electronically. So 140Amps peak. It will draw far less almost all of the time. But will peak at a maximum 140A potentially as you make it work hard.

Let me ask, if I found a Lithium battery with a 70a discard rate, that fit my battery space, would I be able to just drop them in and go??? Would it require a different charger? From what you guys have said it doesn't sound like a simple swap out is possible.

The battery you chose is LiFePO4 and can do a realistic 1C and so that means that it can do 50A max continuous. And possible 100A pulse. It may "work" right now if you dont load the chair heavily. Or it might not. Even if you find one that can do the 140A you need, then it wont last long. Why? Because lifepo4 gives 10 years or use if:
1. Charged very accurately and kept below 3.600V per cell. A fraction higher and you can forget about long life. And the BMS internally will bounce the cells way higher than this for hours as its feeble balance system tries to balance the cells during charge. Its the nature of how they work. So there isnt a better BMS its simply in the wrong place! So its useless for good carging. And we dont WANT any of its other "features"...
2. Is not worked hard. By which I mean doesent have to produce high currents per cell. Because the pack isnt really big enough for the load. In this case its too small.
3. Doesent get discharged deeply. A BMS cutting off power at the fully discharged level, is 100% and then some, discharged. This too means a harder life.
So its very unlikely to ever reach those advertised figures in this application.

To give the lithiu cells a easy time you just need to fit more Ah. A 150Ah pack will need charging weekly. Doesent need to be discharged deeply. And can be charged with a cell balancing charger that garanteed no cell ever exceeds 3.600V or less. While still fully charging the pack.
In this way you also have a pack with 3x the current capability. So you are not working it hard as it can do a peak 150A and 300A intermittent. So the average discharge rate is 3x lower. The result is 3 to 6k cycles, no BMS damaging cells on charge and maybe 10years calender lifespan. And 5x the range of lead. And it fits the same space, costs the same approx.

I'm not ready to tackle building my own setup yet, just put these MK 40's in, so I got a while to think about it. I would be interested if you know of a good tutorial for a beginner like me.

Yes This site. You will not find anything useful or accurate on youtube!
Just ask, and read the many existing threads.

The fact that you have now put the bigger lead batteries in will make an enormous difference.
But you are already shortening their ives by using a nasty mobility charger. They are gel. They must be charged with a charger that never exceeds 14.1V per battery or 28.2V max for both. And they need to sit at that voltage (at 20 Centigrade) for 8 to 12 hours. Followed by 16 hours at FLOAT voltage of 13.4 to 13.5 (27.0V max) afterwards. For a COMPLETE charge. If not then you are killing them fast! And all mobility chargers do at least one of those things wrong! But thats another thread. Ask if you care!

[wes4dbt]

Wow, that's a lot to digest. Hell, now I got to go find my charger specs. lol

I'll probably be back for more info on the what's the correct charger for my batteries. These dam things are expensive, would like to get the most out of them.

Thanks again

[ex-Gooserider]

Welcome to the forums here - one minor suggestion, it helps to go to the "User Control Panel" (link near the top of every page), and put at least your country in the location field... This is a very international forum and it helps us make more useful suggestions and so on, if we know where you are from.

This is also a very technical forum, and it can be overwhelming at times, but don't be afraid to ask questions...

The quick explanation for why the "mobility brick" chargers are a problem is that there are several different types of lead battery construction, and each needs slightly different charging voltages, and so on. The mobility chargers try to be a "one-size-(doesn't)-fits-all" solution resulting in them being 'wrong' for all the different types. They are close, so they sort of work, but because they don't do the exact voltage needed, they will typically give you less battery life in terms of charging cycles than the manufacturer says you should expect.

The MK gel batteries are about the best you can get for lead bricks, but as noted your chair will be working them hard because of their small size. The best way to keep them going for the longest time possible is to "Charge early, Charge often" If you use the chair AT ALL charge every night.... If you will be sitting for a while in one place (eating, using computer, etc....) plug in and charge while you are doing it.

If you look at the technical documentation on your batteries, there is a graph that shows how many charge cycles you can get at different 'depths of discharge'. Lead likes to be kept fully charged, and if you never discharge deeply you will get many hundreds or even thousands of cycles... If you discharge to the rated 80% you might get 500 cycles if you are lucky... If you run them all the way down, you might kill them in as few as 10 cycles....

The 'charge level' LED's on your controller are nearly worthless for several technical reasons, but speaking roughly, if you avoid ever letting your chair get into the yellows, your batteries will live a much longer and happier life.

ex-Gooserider

[wes4dbt]

Thanks for the reply,

I see you have Pride chairs so you are familiar with the crappy charge level indicator. With my current chair the indicator basically stays at full charge. If it comes off full then I only got @ 1/4 mile before I hit the red. My guess the batteries are at @ 85% discharge before it comes off full charge, so I really don't know how much I normally discharge the batteries on an average day. I have looked at the MK spec sheet and if I could get 500+ cycles I'd be very pleased, my other batteries were not MK's so I'm hopeful. I am faithful about charging the batteries after each use.

In the last few month my should has finally decided it can't take no more (I'm 44yrs post) so I'm going to start using my electric around the house in hopes it will help with the pain. Meanwhile I'm looking around for a quality used chair (for @ $4,000) with groups 22 batteries or at least NF22. I like the Permobile M3 or the Quickie q700 series. The problem is most of them have a lot of things I don't need, like tilting, but I do like the elevate, that's why I bought the Air 2. It was only $4,000, new

Anyway, thanks again

[Burgerman]

You really dont want 22nf as thats too small if you expect a decent service life.

Also so you understand quite how important tiny charge voltage differences make, this is a MK graph. Warning you not to charge above the specified 13.8 (27.6V) to 14.1 (28.2V). So at room temperature the correct charge voltage is say 13.95V (27.9V) as thats bang in the middle. Most generic mobility chargers are 14.4V (28.8V) so they can charge both gel and AGM type lead batteries.

Heres what it does to your cycle life. And NOT completing a full 16 hours or longer is equally as bad!

0.7 of a volt, reduces your 500 cycles to about 8 months. Instead of 1.5 years or so. Not doing a full 16 to 20 hour recharge, and thinking its "done" when you get a green light, will cost you capacity over time too, further shortening cycle life.

[wes4dbt]

Thanks for the chart but not sure how you can get a 16 - 20hr recharge if you use your chair off an on both day and night. Only 24hrs in a day. As for the charger, I'll check out chargers just for 24v Gels?

[Burgerman]

You cant if you use it daily. And thats one of the main reasons that gel batteries will never give you 500 cycles.

But you CAN leave it connected as long as possible on certain days - make a point of doing so weekly and have more than one chair.

And you can use a more powerful charger to get the initial bulk charge completed faster leaving a longer time for float.

And you can plug in during the day whenever you get chance to decrease the average depth of discharge generally. This is also a good reason why you should never have used anything but the biggest battery that you could fit.

And all of this above helps! A lot!
And you can check your charger doesent exceed 28.2V ever during charge with a voltmeter. If so, get a different one that is gel freindly. Which again is not easy.

[expresso]

https://battery-chargers.com/

you can call them and ask for the set voltage you want - i believe they can make the changes - i never have tried that

i have used there 20A chargers before when i had lead - and i also used a Salmex Marine Charger which came close to Gel specs for charging

[Rollin Positive]

I dont see that anyone has addressed why your batteries only lasted 6 months and you dont used it that much?

In till you figure your options are you still charging it every day?

The Air 1 and 2 are really small minimal use chairs so you should get a years worth out of them

That said Pride claims 19 miles per charge? Have you tested them and see what you get or they just die that fast?

I think Pride has a year warranty on them so at lease look for replacements if you got the chair new

Also agree with BM Prides chairs that use the NF22 only get 6-8 miles tops

If your looking for a chair and need miles look at a Permobil m300, F3 these support group 24 batteries from MK about $500 plus shop around or on line but dont buy from Walmart when your talking mobility. 13-18 miles per charge based on your weight, driving pattern etc.

If you are on Medicare or private insurance why not buy new mine only took 45 days from start to delivery message me I can help right expresso!!

If you buy used make sure you get your width and seat depth correct
Sacramento, California
https://www.ebay.com/itm/2016-Permobil- ... SwHbpf8Ps~

https://www.ebay.com/itm/Free-Shipping- ... SwWDBgJf3g

Color change on these chairs is really easy and cost $15

https://www.ebay.com/itm/Free-Shipping- ... Sw8W9fq1Cz


https://www.ebay.com/itm/Permobil-Corpu ... Sw199gLbJ7

[Burgerman]

On most chairs, like mine (every one of them is different) the seat depth and width is adjustable within a wide range. Just slaken a few allen bolts and it can be any width or depth you choose. Are permobils not the same?

[wes4dbt]

Thanks for the replies,

If your chair comes with a 5a charger is it safe to use a 8a or higher??? I've always worried that you might burn out the wiring or it might ruin the batteries. If I could use a 8a charger that probably would help.

Yeah, Permobile seats width and depth are adjustable. My issue is the massive seats (they look 5 or 6" thick) and backrest. It makes the floor-to-seat height higher than I like and the backrest look like they would restrict your movement, but I've never had one so I'm not sure.

[wes4dbt]

But you are already shortening their ives by using a nasty mobility charger. They are gel. They must be charged with a charger that never exceeds 14.1V per battery or 28.2V max for both. And they need to sit at that voltage (at 20 Centigrade) for 8 to 12 hours. Followed by 16 hours at FLOAT voltage of 13.4 to 13.5 (27.0V max) afterwards. For a COMPLETE charge. If not then you are killing them fast! And all mobility chargers do at least one of those things wrong! But thats another thread. Ask if you care!

Was looking at the spec sheet for my batteries,

Cycle 13.8 - 14.6 volts
Float 13.4 - 13.6 volts

Does that mean the max charge should be 14.6 and the max float 13.6

[Burgerman]

No thats a SELL sheet! Thats what your mobility charger does. Its the limits of what you could use.
Thats so they sell batteries to anyone with any old charger.
Does it work? Anything will charge them. 15 volts? No problem! Does 14.6 give you the best cycle life? Nowhere close! Probably only HALF of what they can do. So maybe 250 cycles? Maybe less if you take them off charge when you see the green light! Because undercharging also means grid corrosion and permanant sulfation on top of the damage caused by over voltage. And complete charge takes 20 hours.

Heres the real deal.
MKs own technical data. For GEL
READ THIS VERY CAREFULLY...
http://www.wheelchairdriver.com/MK0.pdf

Heres the differences between GEL and AGM batteries...
Read carefully!!!
http://www.wheelchairdriver.com/MK2.pdf

DETAILS MATTER!!!! Theres no such thing as a charger that charges AGM and GEL batteries unless it has two seperate switchable settings. Or completely custom user settings.


If you dont understand any of it, ask! I because I do...

It tells us these things.
Charge at (at room temp) 13.8 V to 14.1V MAXIMUM for fastest charge rate.
Keep doing that until CURRENT falls to a very low level - typically takes 8 hours to 12 hours. Then drop voltage to a lower float voltage and continue indefinately. Which finishes the charge over the next 8 to 10 hours and keeps them ready to use.

If you always do this, ACCURATELY and never discharge below 80% capacity, then you will see 500 cycles (before end of life, where they only supply 80% of original rated 20 hour rate Ah.)

If you do what most mobility chargers do, and discharge them heavily as you were doing, you will get a few months use and crap range. I tell people this for 23 years and nobody listens!

[wes4dbt]

If you do what most mobility chargers do, and discharge them heavily as you were doing, you will get a few months use and crap range. I tell people this for 23 years and nobody listens!

Oh, I think most people listen, maybe they don't understand but they listen. I asked a second time because the sell sheet, which I mistook for a spec sheet, seem to be saying something different. Sometimes it takes hearing things more than once before you understand.

Thanks for the information

btw - I'm still interested in information on this question,

If your chair comes with a 5a charger is it safe to use a 8a or higher??? I've always worried that you might burn out the wiring or it might ruin the batteries. If I could use a 8a charger that probably would help.

If I buy a new charger, I want it to do the best job.