New MK batteries seem drained

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New MK batteries seem drained

Postby amm » 06 Oct 2019, 15:10

Hi everyone

I bought some new MK 40 AH GEL batteries for my spectra plus wheelchair. I bought them on August 8th, so they have had a few charges to settle in. They were both balanced by connecting them together for 12 or 14 hours before installing, and the first charge was 12-13 hours, and each charge is usually roughly 9-11 hours per night. Most days I don't leave my house, and if I do, I do less than a mile.

Usually when I get new batteries the whole chair feels refreshed, slightly faster, I notice much better acceleration and decellartion and the torque on hills etc is improved.
However, with this new set, acceleration is still sluggish, torque is definitely much reduced, and the batteries run out quickly.

What could be the cause of this, and any suggestions as to what to do?
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Re: New MK batteries seem drained

Postby Burgerman » 06 Oct 2019, 15:27

40Ah is too small to use as an outdoor battery with a full sized human to move around. I am not at all surprized you see problems. Remember that it uses more power shuffling around indoors than distance outdoors. Its easy to use half the battery inside a house if you keep turning left right, as thats where the high amps get used. Rolling at speed is the lowest battery load.

The more you work a lead battery the faster it deteriorates.
The greater you discharge it each cycle, the faster it dies.
The faster its capacity is diminished, the greater the average discharge level it sees every time it is used.

The real answer is that large 74Ah MK gel batteries have just about got the ability to survive a while, if topped up straight away, and never discharged too deeply. Like avoiding hills...
Also if you can feel a difference between old batteries and new thats because of internal resistance being too high. The internal resistance of a new battery is low. The internal resistance of a 74Ah battery is HALF that of a 40Ah one. So twice as good. The reason you notice it is because the batery is too small for its job.

Fitting a set of 40Ah batteries is then a perfect storm if you try to go far, climb a hill etc. And once the deterioration begins it accelerates rapidly faster and faster.

You could test the batteries for capacity with the PL8. Reject them if either shows less than 80% capacity.
You could measure the voltage drop under load, and reject them if either is lower than a new fully charged MK gel.

But they will fail both those tests.

Why are they worse than previous sets? Because motors become less efficient as they age. Tyres become harder to push, if solid, or users gain weight. So the rapid death spiral happens sooner. The batteries would be exactly the same as the previous set. Unless one has a fault. Measure voltage drop under load on each INDIVIDUALLY and compare.
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Re: New MK batteries seem drained

Postby Burgerman » 06 Oct 2019, 15:39

Theres another possibility.

Many users like me murder batteries, and after a few months detect they are not as good as they were. So replace them. If a dealer was to do that, he then has my old worn batteries, that are say 8 or 9 months old. And look like brand new. Its very tempting for him to sell those AS NEW and make a free 500 pounds, because many users that are like you, light users, will never be able to notice for another 5 years because you dont go far. And not all are honest.

Its already been PROVEN that this has happened "by accident" several times on here. Complete with new boxes etc.

So how do you know they were not used? It appears that this is a common scam.
Wouldnt happen to me because I fully charge, and MEASURE capacity before installing. Maybe 2 or 3 50% cycles, then test. If I dont see say 70Ah from a 74Ah gel, they would go straight back.

____________

Also, if you never go more than a mile, you SHOULD go far enough to discharge them to around 30 or 40 percent before recharging them now and again when new, because this is what 'FORMS' and etches the plates and gives them the lead dioxide coating. So go some serious distance once or twice and then see what happens. Also COMPLETELY IGNORE those stupid battery lights on your control pod. They are meaningless.
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Re: New MK batteries seem drained

Postby flagman1776 » 06 Oct 2019, 20:30

If I'm reading this right, the most powerful battery option is only a 50ah MK. My experience is only the biggest option should be installed, that it pays you back in better battery life since the battery is less stressed.
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Re: New MK batteries seem drained

Postby flagman1776 » 07 Oct 2019, 01:54

It's a long shot but possibly the connections weren't cleaned properly. I don't suppose it was wired incorrectly.
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Re: New MK batteries seem drained

Postby Irving » 07 Oct 2019, 07:53

flagman1776 wrote:If I'm reading this right, the most powerful battery option is only a 50ah MK. My experience is only the biggest option should be installed, that it pays you back in better battery life since the battery is less stressed.


yes, in a spectra 50Ah is biggest you can fit but in a MK that's an AGM not a Gel.
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Puma 40 backup, 73Ah MK (for now)
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Re: New MK batteries seem drained

Postby Burgerman » 07 Oct 2019, 08:59

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Re: New MK batteries seem drained

Postby Dan » 07 Oct 2019, 10:50

I have a Sunrise Salsa M2 with rise, tilt, recline and electric legs that only gets cheap batteries fitted. It gets used everyday in house and also outside shopping at least twice a week. About a mile around the house per day plus outside shopping, the batteries can easily last over a year and a half.

https://www.amazon.co.uk/Haze-HZY-EV12- ... B01D3JEI7U
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Re: New MK batteries seem drained

Postby LROBBINS » 07 Oct 2019, 11:34

How much do you weigh?
Does your house have smooth or difficult (e.g. carpeted) floors?
Do you do a lot of quick turn-in-place maneuvers?

All sorts of things affect battery drain, and with driving just 1 mile a day one can certainly expect a long battery usable life especially if you don't ask them to do "difficult" things such as rapid acceleration, going over difficult thresholds or other obstacles, climbing ramps, or turn-in-place. You could easily find that older batteries are still quite good for your use case, but that the chair is no longer up to the task if asked to do these things. Expresso, who likes to take 50+ mile drives and negotiates New York city's difficult streets and sidewalks would have a very different experience, and indeed has moved over to large capacity LiFePO4 batteries because even the best lead batteries simply can't work for him.
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Re: New MK batteries seem drained

Postby Burgerman » 07 Oct 2019, 11:43

Also, mid drive turn in place takes WAY less amps to do, than a nose heavy rear drive.
Typically 25 to 40A at most.
But 100 to 120A in an otherwise identical rear drive chair. Thats every tie you turn say 10 degrees to the right...

Theres so many variables that it is not possible to make such a comparison in any meaningful way.

Plus, its easily possible to fully drain a battery in a day indoors. But only use 25% of it on a 5 mile run on LEVEL ground at constant speed.
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Re: New MK batteries seem drained

Postby Dan » 07 Oct 2019, 12:32

I'm not really that light at six foot tall and 75KG. My floors are mostly not carpeted and I know that makes it a lot easier for an electric chair. I do move about quite a bit with many stops and starts per day.

The chair has 4MPH two pole motors which has enough torque for me to stop and start on any ramp I have tried it on. I have gone up ramps that are so steep I had to lean forward to stop the chair tipping.
The chair also has hard tyres, R-net and is now nine years old. A lot of the time its only charged up every other day.

I just thought I would post a different perspective on battery life and use. I also I an outdoor chair.
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Re: New MK batteries seem drained

Postby Burgerman » 07 Oct 2019, 12:50

Your weight is half of mine. That means the all up chair weight is around 33% lighter.
2 pole motors, 4mph take around 33% less amps at every turn, every movment. All of the time.

So you are taking 66% less out of your battery than I do, even if we move the same exact way.

But we dont.
I MURDER batteries due to the way I move, and the programming. I would estimate I take at least double the power from them simply due to the way I drive.
Thats means you take another 50% less than me... http://www.wheelchairdriver.com/gopro/control.mp4

So during 1 hour, indoors alone, I likely take hundreds of amps, many many times and take 30Ah from the battery.
You likely take just a few tens of amps peak, and take 5Ah from the battery. (weight, 2 pole, 4mph gearing, mid drive)

If you have a 40Ah battery and take 5Ah from it you likely do you will get any thousands of cycles and many years.
If you have a bigger 70Ah battery, and take 30Ah out of it at high current as I do daily, its basically used up (peukert) and shows as a low battery. After ONE hours use!

If you do that to a battery every day it will die in a few months. And I do.

This is to try to show how difficult it is to compare. Its not actually possible. And that is also without even considering other variables. Considering that incorrect charging that a mobility charger provides will easilyreduce service life by 70% if its just a few fractions of a volt high. Or another unknown amount if it stops charging early as they all do.
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Re: New MK batteries seem drained

Postby Rollin Positive » 09 Oct 2019, 02:53

amm wrote:Hi everyone

I bought some new MK 40 AH GEL batteries for my spectra plus wheelchair. I bought them on August 8th, so they have had a few charges to settle in. They were both balanced by connecting them together for 12 or 14 hours before installing, and the first charge was 12-13 hours, and each charge is usually roughly 9-11 hours per night. Most days I don't leave my house, and if I do, I do less than a mile.

Usually when I get new batteries the whole chair feels refreshed, slightly faster, I notice much better acceleration and decellartion and the torque on hills etc is improved.
However, with this new set, acceleration is still sluggish, torque is definitely much reduced, and the batteries run out quickly.

What could be the cause of this, and any suggestions as to what to do?


Sorry MK batteries suck...I am not sure what they have changed in the manufacturing process but I am betting its something.

To make it worse MK itself is the worse! 3rd set of MK 24's 1st set lasted 2 weeks and it one had a bad cell, 2nd set same thing, but not only did MK require the DME to do a week test on them and they failed then MK had to come get them and do the same test!!!

So now on 3rd set and sure enough they start dieing and not getting close to the miles I use to get.

Chair went through complete check out and DME even required me to put new motors in and get a new charger and it still didnt help.

So MK came and got the batteries to retest again and didnt find an issue and show holding a charge of 90%

But put the batteries back in and get 3 to 4 miles vs 13+ when they ran right.

I dont think any brands manufactures ship with MK anymore so they have lost a big market share in the US.

There sales manager Jason hes a real interesting guy seems more interested in selling product then standing behind the product after the sale.
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Re: New MK batteries seem drained

Postby Burgerman » 09 Oct 2019, 04:30

You keep repeating this. Yet when actually measured, and correctly charged, after a few full cycles they are the same internal resistance, and Ah as ever. Measured accurately at the 10 or 20 hour rate. And I actually MEASURE them. So its not just hearsay, or urban myth, or personal testimonial. Because thats alost eaningless and too any variables. I dont GUESS at a batteries performance, by
'feel and opinion I MEASURE it. Its simply not true as far as I can tell. Maybe the ones you are getting in the US are different... I dont see how.

If a 73.6Ah MK measures 73.6 its as good as new. If it measures less, its deteriorating. All batteries do that. After 500 cycles, under CONTROLLED conditions, and discharged by 80% of its reMaining capacity MK gel will deliver 500 cycles. But after just half of that, you will should notice a lot less range. So 7 or 8 months, with heavy use will kill them. 2 weeks of over discharge, or bad charge parameters will also murder them.

Anyway, at the current prices, they are comparable with a set of lithium cells. Lithium is CHEAPER Ah per Ah now. These have got to the point where we can now fit 16 105Ah cells, in the place where the old useless lead bricks used to be. Giving 10 years worth of service and total usable 210Ah! And the same DISTANCE in miles as 8x grp24 MKs.

Using older lithium technology, in the heavy old bounder, with 'only' 160Ah available, expresso gets around 68 miles (not 7 or 13!) as shown below. So arguing about which lead bricks are best is like arguing about the best type of coal to put in your car. Lead is DONE! Finished. Its totally useless in any modern heavyweight powerchair. We are in 2019 now.

With the newer 210Ah option now possible, that would be around 90 miles. And it will all fit in place of the MK. but 68 realworld miles isnt bad.
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Re: New MK batteries seem drained

Postby amm » 24 Oct 2019, 12:34

Hi

Sorry about the delay in replying, it has been a busy time, sadly with a funeral.

I have actually lost weight since the last set of batteries (not loads, just half a stone, making me roughly 11stone/ 70kg now)

There is one room with short carpet in my house, the rest is wood. The amount I use it indoors is very small, I don't do loads of moving about really.
the main issue is going up slopes (which i realise a 40ah battery will always suck at, but before with new batteries, it would do them fine) especially in to my WAV, which is why I notice it so much.

How would I measure them to see if theyre the right levels?

Should i contact the shop to let them know that i suspect that there are issues with the batteries?
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Re: New MK batteries seem drained

Postby Burgerman » 24 Oct 2019, 13:23

Your batteries may just require formattint, or forming. They are new but have never been discharged. Discharge them by 20 or 30Ah. Then recherge, and then test. They sound like they have never been adequatly used to form the plates.
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