MK Batteries

[crypmanii]

My wheelchair currently runs on 2 MK M24 SLD G batteries. When I last replaced them, less than 1 year ago, I wound up getting an off name brand that was "supposed" to be a comparable replacement however they have not lived up to the task. Before I spend $300+ per battery does anyone have any decent recommendations for replacement that will last and don't cost a fortune or a website that sells the MK batteries for a little less. I realize you get what you pay for. Just figured it was worth looking into. I'd love to replace them with a Lithium pack, which I realize will cost more, but I don't really have the ability to put something like that together and haven't seen where I could just buy them online already wired and ready to go.

Thanks for any advice

[martin007]

Where are you from?

[crypmanii]

I live in New Jersey, USA

[Burgerman]

1st what were these batteries exactly? What chair? What are you charging it with?

The MKs are good IF CHARGED CORRECTLY!
The cheap ones you bought may be and probably are junk.
The only batteries that will match the MKs are the GEL version of the HAZE 80Ah which will again match or beat the MK.
https://www.ebay.co.uk/itm/131119213209

But while you say you dont want lithium, 8 of these will fit, give you 5x to 6x the range, as well as at least 15 years of use. Probably longer.
https://shop.gwl.eu/LiFePO4-cells-3-2-V ... html?cur=1

You cannot buy these ready to go. It will take a little learning and some work. But there are a few on here that hadnt a clue and have now built more packs than I have. Like expresso... He does 80 mile trips around new york now.

[swalker]

I bought my last set of MK batteries from https://buildmywheelchair.com/. This is fourth order I have placed with them (tires, batteries, and motors all for a Permobil F5).

They have been easy to deal with and have provided excellent service. They have had the lowest prices for each Item I have purchased from them.

The only negative is that their website indicates there is a 30% restocking fee. So, be very sure that you are ordering the correct part if you buy from them.

The MK batteries were drop shipped from MK, so there is not much chance of having received counterfeit or used batteries.

Steve

[Burgerman]

Are the Haze Gel 80Ah batteries available in the US/Canada?

They are actually a better bet now than the MK for price reasons and because they are one of very few batts that can match the MK gel for performance. They actually have 9% better capacity, a slightly less cycle life figure (which will actually be superior in use because they are bigger so lower average depth of discharge) and very similar measured internal resistance (measured as AC impedance by myself). Actually mine measured identical to MK. And a little extra range.

And a close match (on specs) are the Permobil branded batteries, which look to be pretty good too. Not sure who make those (permobil dont make them) but specs are good. Treat as Gel for charging. They are both AGM seperators and gelled electrolyte recombinant valve regulated same as the MK/Haze ones.

[swalker]

The Haze batteries do not appear to be readily available in the US.

To buy them in the US, it appears we must purchase from a vendor outside the US and have them shipped.

I have had good luck with the MK batteries, though it was my intention to switch that wheelchair to using LiFePO4 cells when I last replaced the batteries with MK Gels in May. The reason I went with MK lead acid gel batteries is that I have had trouble finding a reliable supplier of LiFePO4 cells.

I am continuing to search for a reliable source of LiFePO4 cells in the US. The last time I bought them I ordered them from China. I received used cells. Since the cells were bulged, there was no legal way to return them to the seller. I installed them in my X4 wheelchair and they have performed OK, but I don't want to go through that again.

It is legal to ship damaged LiFePO4 cells within the US, but not overseas. Therefore, I want to buy from a vendor that ships from and accepts returns to a US facility. There are not yet many options available for that.

Steve

[Burgerman]

Isnt there a GWL in the US?
https://shop.gwl.eu/LiFePO4-cells-3-2-V ... html?cur=1

[swalker]

I have not found a US source for GWL cells. If you come across any, please let me know.

Steve

[crypmanii]

1st what were these batteries exactly? What chair? What are you charging it with?

The MKs are good IF CHARGED CORRECTLY!
The cheap ones you bought may be and probably are junk.
The only batteries that will match the MKs are the GEL version of the HAZE 80Ah which will again match or beat the MK.
https://www.ebay.co.uk/itm/131119213209

But while you say you dont want lithium, 8 of these will fit, give you 5x to 6x the range, as well as at least 15 years of use. Probably longer.
https://shop.gwl.eu/LiFePO4-cells-3-2-V ... html?cur=1

You cannot buy these ready to go. It will take a little learning and some work. But there are a few on here that hadnt a clue and have now built more packs than I have. Like expresso... He does 80 mile trips around new york now.

I typically use the MK, M24 SLD G batteies.

I'm running them in an Omegatrac.

And I'm just using the charger that came with my wheelchair to charge them.

I would love to do a lithium battery pack. Unfortunately with my physical capabilities I'm not able to do all the wiring that I think is going to be required.
Thanks for the information tho. I’m definitely going to do some research.

[Burgerman]

I dont know what your charger actually does. but I never saw and measured any mobility charger that came close to what is really needed. Some are better than others. Most are really designed for AGM but claim to charge gel too. But while thats possible it cannot be automatic so it would need a way to set it for gel. But its highly likely you are getting about 1/3rd to 2/3rds the possible service life that they CAN do when properly charged. I have a bunch of chair chargers colleced over the last 26 years. They are all on a shelf quietly rusting away in my garage. I cannot afford the batteries to be using them. And they are all underpowered too. I mostly charge lead at 12A via XLR or 25 to 40A via Anderson connectors. That does NOT speed up the charge by very much. Although it puts the bulk of the charge back faster. And so great for mid day splash and go charging. What it does do is to allow a more complete charge in the limited overnight period we have available. Which results in a longer service life and so full range for longer.

[crypmanii]

I dont know what your charger actually does. but I never saw and measured any mobility charger that came close to what is really needed. Some are better than others. Most are really designed for AGM but claim to charge gel too. But while thats possible it cannot be automatic so it would need a way to set it for gel. But its highly likely you are getting about 1/3rd to 2/3rds the possible service life that they CAN do when properly charged. I have a bunch of chair chargers colleced over the last 26 years. They are all on a shelf quietly rusting away in my garage. I cannot afford the batteries to be using them. And they are all underpowered too. I mostly charge lead at 12A via XLR or 25 to 40A via Anderson connectors. That does NOT speed up the charge by very much. Although it puts the bulk of the charge back faster. And so great for mid day splash and go charging. What it does do is to allow a more complete charge in the limited overnight period we have available. Which results in a longer service life and so full range for longer.

Thanks for the information Burgerman. Do you have a specific charger that you would recommend that would still be compatible with the XLR port on my VR2 Joystick?

[Burgerman]

There is only one correct way, and thats this:

www.wheelchairdriver.com/MK1.pdf

Which boils down to this for a GRP24 74Ah battery or rather 2 in series:
TWO methods where the first is the fastest:

This is stage 1. CC (Constant Current) stage. Charge at up to 24A (where the higher this figure is the better in cyclic use because TIME is the problem). But we cannot charge at more than 12A via the XLR connector. So 12A Max it must be. So set to 12A.
Continue until voltage climbs and reaches 28.20V at 20 Centigrade.

Stage 2. Current will now start to drop progressively over the next 8 hours while voltage remains at exactly 28.20V. Stage 2 is called CV. (Constant Voltage). This stage ends after 8 hours at this voltage or when current falls to 100mA whichever occurs first. At this point its fully charged. Total charge time will be Stage1 + 8 hours. This is for cyclic use. Not for a top up of a nominally full battery. However many chargers cannot be set to end CV in this way. So in that case we need to use the slower method which adds a 3rd FLOAT stage.

Stage 3.Float stage. Everything as above, but terminate stage 2 CV charge (above) at 300mV approx if possible, which occurs many hours sooner. Many chargers do this at a too soon point like 1A. And it will take a different amount of time to reach this point depending on discharge depth. NOW Float! In the absence of the ability to set stage 2 as above we need Float! So now drop the charge CV voltage to a lower 27V to 27.2V indefinitely. And allow the Float stage to top up the battery to the 100% point instead. However this means total charge time will be around 20 hours or longer. Charge can continue safely for a week at this voltage.

[Burgerman]

As it happens I am in the middle of charging a set on Gel batteries (80Ah Haze) right now. These like all gel batteries require the same charge algo.

This is what it actually looks like.

So far I have been charging for x hours.
Current has fallen from 12A CC down to a low 165mA. It will take a further 4+ hours to drop to 100mA or 8 hours at CV whichever occurs first.
Voltage is being held steady at 28.20 volts.
19500mAh (19.5Ah) has been returned so far. In 5 hours. About 98% charged. It will take another 4 hours and a bit to return that IMPORTANT 2%. Without that some lead sulfate will remain on the plates shortening the life and reducing capacity every charge.

Real time graphs and data from the PL8 charger I am using. There will be no need of a float stage here!

[Burgerman]

After almost 8 hours, 12A charge, 20Ah (well 19902mAh) returned, (quite a small recharge since around 45Ah is usable on an 80Ah lead battery) current has dropped to 100mA. Thats the termination point. Charge then ended. Thats 1 hour CC (@12A) and 7 hours CV@28.20V. If it was deeply discharged it would have taken the full 8 hours at CV and maybe 3 hours at CC before this. So charging with this 2 stage algo is faster than a 3 stage one with an earlier termination but longer Float stage.