Which battery do I need please?

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Which battery do I need please?

Postby LearnerDriver » 15 Feb 2021, 23:24

A stupid question from a newbie, well what else do newbies do LOL.

Invacare TDX SP2 narrow base, what size batteries do these take please?

Also what brands would people recommend and also any good places to buy from?

Thank you.
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Re: Which battery do I need please?

Postby martin007 » 15 Feb 2021, 23:46

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Re: Which battery do I need please?

Postby ex-Gooserider » 15 Feb 2021, 23:47

It should be listed in the manual, but probably either Group 24, (hopefully) or Group 22NF (won't go as far) If wanting to stick w/ lead bricks, we recommend MK GEL NOT MK-AGM!) for most users or Odyssey for those that tend to want more performance. Better but more effort is to do a conversion to Lithium Iron Phosphate (LiFePO4) cells. The conversion takes moderate amounts of work, and is more expensive up front, but gives much more range and far longer life from the batteries so the long-term cost is MUCH lower.

Lots of threads elsewhere on how to do the conversion...

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Re: Which battery do I need please?

Postby LearnerDriver » 16 Feb 2021, 22:04

Thank you for the replies. :worship

I am sure there are lots of things about converting to lithium but please can you help me find a really easy to follow topic that a newbie will be able to follow. You long term folks on here know stuff that seems simple, to you but is like rocket science to some of us.

Also are there any recommended online suppliers as I can’t see us being allowed to go out shopping any time soon.
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Re: Which battery do I need please?

Postby Bubbernator » 17 Feb 2021, 04:14

I strongly recommend this book.
https://www.amazon.com/DIY-Lithium-Batt ... 0989906701
It starts at the beginning and covers different types of lithium batteries and their applications.
It is a practical users guide, not a theoretical textbook.
That being said, be sure to read all about the potential dangers involved in using certain types of batteries.
Most of the folks here use a lithium iron phosphate type of battery (which is much safer than a lithium-ion battery pack).
Don't be afraid to ask a lot of questions. There is plenty of experience on this message board that can help you avoid expensive mistakes.
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Re: Which battery do I need please?

Postby rover220 » 17 Feb 2021, 07:08

22nf git the narrow base
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Re: Which battery do I need please?

Postby Burgerman » 17 Feb 2021, 11:53

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Re: Which battery do I need please?

Postby rover220 » 17 Feb 2021, 12:13

Fit rather :dance
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Re: Which battery do I need please?

Postby Burgerman » 17 Feb 2021, 14:02

When you get them remove from boxes. Resist the temptation to lick the terminals. Use a voltmeter. If either battery shows less than 12.6V I would send them back. If above 12.6 volts then do the following. Connect together - positive to positive. And negative to negative. Nothing will apear to happen. Leave them this way for 24 hours. Longer if you have time.

That means they are then at the exact same state of charge. Balanced. So that when you use or charge them you dont end up overcharging one and undercharging the other. When installed, put on charge for at least 24 to 48 hours and ignore the charger saying its done. Its not. Then use as normal. No special break in is needed but they will get slightly better over the first 10 to 20 cycles. And then they will start to deteriorate... Just avoid fully discharging for the first few cycles. And if you have any sense avoid doing that anyway!
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Re: Which battery do I need please?

Postby LearnerDriver » 17 Feb 2021, 20:24

OUCH, I wasn’t quite expecting that price per battery.

Oh and as for licking the battery terminals, it’s not a PP9 and considering how far apart the terminals are if I could lick them, I would be so very popular with females LOL.
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Re: Which battery do I need please?

Postby Burgerman » 17 Feb 2021, 21:27

Battery prices...
Dont pay VAT.

But you get what you pay for. Theres only really 2 batteries on the market and rebrands of them, that can stand up to heavy traction use. And not die fast.

That means for extreme use, best torque fast recharge, etc the Odyssey line.
It means for normal people the MK Gel (NOT MK AGM) line.
Or the slightly lower quality sonennschein A500 dryfit batteries, they cheapened them a few years back and they offer less cycles now.

Non of these are cheap. But they are still cheaper than using anything else which are worse!

The problem in your case is that 22NF sized batteries are inadequate for a heavy daily use. They get discharged too deeply as they are not of adequate capacity. So this is always going to be a problem as every chair with 22NF sized batteries is going to struggle for range and kill the batteries twice as fast. The bigger GRP24 or 73Ah gel batteries dont fit your chair. But those will last way longer. Because you will discharge them less deeply each day. And so average level of discharge daily is a lot lower. This makes a huge difference.

Yes theres hundreds of cheap chinesium lead batteries around at half that price. But they are less than half as good. So at the price of decent lead batteries, you can get 5x the range with lithium ion phosphate. But thats a learning curve and a bit of work. And hard to get a decent charger for the moment. Out of stock for a year. So... You have 3 choices. Go on eBay and buy cheap 22nf batteries. And get what you pay for. Or MK 22NF for the moment.
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Re: Which battery do I need please?

Postby Burgerman » 17 Feb 2021, 21:39

You could for e.g. buy a set of these. https://www.careco.co.uk/item-p-ms08008 ... h-battery/

Save a fortune. But be aware that they will perform worse in regards range. And in regards torque. Because they are higher internal resistance. That also means they will sag of drop off fast on hils for e.g. And they offer a 300 to 350 cycle life at 80% DOD compared to say the 500 to 550 from the MK Gel.

Choices! Remember that because you are using a small 22NF sized battery that you are giving it a much harder time and will notice these differences way more anyway. Make sure the next chair is a 75Ah/80Ah grp24 battery!
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Re: Which battery do I need please?

Postby LearnerDriver » 18 Feb 2021, 20:37

Having the narrow base version of our chairs isn’t ideal but it does make life easier when you have an assistance dog at your side.

What I was struggling to work out is where to buy some of the Odyssey or the MK Gel ones you recommend either locally or online from a known good supplier Any input from you folk would be appreciated.
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Re: Which battery do I need please?

Postby rover220 » 18 Feb 2021, 20:47

LearnerDriver wrote:Having the narrow base version of our chairs isn’t ideal but it does make life easier when you have an assistance dog at your side.

What I was struggling to work out is where to buy some of the Odyssey or the MK Gel ones you recommend either locally or online from a known good supplier Any input from you folk would be appreciated.


hi, i can supply new mk 22nf batteries for you tdx NB. what is your location?
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Re: Which battery do I need please?

Postby stevelawiw » 18 Feb 2021, 23:31

@Burgerman
Battery prices...
Dont pay VAT.

On the careco site you have linked to batteries aren't zero rated, where can you get Vat relief on batteries these days?
I know it used to be possible to not pay the Vat, and I agree that for use in wheelchairs etc we shouldn't have to, but from where can you source them zero rated??
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Re: Which battery do I need please?

Postby Burgerman » 18 Feb 2021, 23:35

Not sure of the names but I frequently come across them on eBay, or many mobility websites.
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Re: Which battery do I need please?

Postby stevelawiw » 18 Feb 2021, 23:41

https://www.ebay.co.uk/itm/Days-Medical-Aids-DMA-Strider-Midi-3-Batteries-X-2-VAT-FREE-LISTING/203150201951?epid=2255535498&hash=item2f4cb2145f:g:jnMAAOSwd4tUCdtC

Yep you're right, they are out there! I'm not saying the ones I've linked to are any good, just that they're zero rated
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Re: Which battery do I need please?

Postby Burgerman » 19 Feb 2021, 08:25

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Re: Which battery do I need please?

Postby LearnerDriver » 22 Feb 2021, 19:00

I keep coming back and reading this thread and am trying to work out the difference between AGM and GEL.

Please can somebody give me some example of what to expect the difference to be as I would want to know if I will get the benefit or not for the extra cash and I imagine the extra cash amount won’t be small.
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Re: Which battery do I need please?

Postby Burgerman » 22 Feb 2021, 19:27

Theres 3 things that matter with mobility batteries.

1. impedance. The lower the impedance the lower the peukert values. And so the further you travel on each Ah... And also the better the battery performs if you have a high load with less voltage drop. Esp when say 50 or 70% discharged.

2. Cycle life. A typical quality Gel battery has around 500 to 550 cycles to 80% remaining capacity compared to when it was new, and when discharged by 80%. AGMs cannot match that figure. If you find one that does, it will typically be much higher impedance... So performs worse. So theres a balance between current producing capability, and cycle life, and capacity.

3. Ah. So a battery that is the stock GRP24 size is typically between 70 and 100Ah. You think you want the 100Ah one right? Wrong! Its 100 UNUSABLE Ah. As soon as you load the battery the voltage drops off. You are very limited in current producing capability. Because the more Ah you try to crap into the same volume the worse the cycle life and or impedance will be.

So its quite possible to get 3 batteries. Identical 260 x 170 x 220mm tall. Thats the Group 24 size.

-One may be 100Ah and have 500 rated cycles. But it will barely move a chair, and cant support high currents. You want to climb a threshold or a curb? Think again. And it will only give you around 30Ah from its 100, before the chair stops as its voltage collapses under load. So all that Ah can only be extracted slowly. Internal resistance or impedance matters.

-Another may be 68Ah like the Oddysey. 2.5mOhm. This is the lowest capacity, and the lowest impedance. It can start a frozen truck in siberia. It has 1500 starting Amps capability for 5 seconds, 780CCA etc. It only offers 450 deep cycles, and only if very thourougly charged daily. This is what I used to use. It alows a chair to respond properly if programmed to do so. And has better torque, faster charging, etc. And higher cost. You will get MORE or similar range than the typical gel battery in spite of less rated Ah due to it being able to support high loads when heavily discharged. In other words at the 2 hour rate it beats the bigger MK gel if worked hard. It will give less range if you spend all day watching TV or going slowly. The advantage of low impedance. The measure of a good battery. Soccer player, heavy weight user, chair programmed to jump on command? This is is the best battery.

The MK gel is designed for high cycle life, medium capacity, and adequately low 3.5/4mOhm impedance for average powerchair use. A good balance for an average user. 450A max cranking amps. Charged properly it will perform adequately to give most normal powerchair users the best compromise and the longest lifespan in cyclic traction use.

All the cheap chinese AGM batteries try to compete. They use lower quality lead, seperators etc. But basically its a 3 way triangle. Ah, impedance, cycle life. Increase one, and the other two get worse. Looking for battery quality?
You are comparing the three things. Impedance first, cycle life second, and ah last. And Ah at the 2 hour rate is more of a useful measurement than anything. Because it takes into account the impedance, peukert values etc.
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Re: Which battery do I need please?

Postby LearnerDriver » 22 Feb 2021, 19:36

That was a fascinating read, I am sure I didn’t understand it all.

So as someone who is home based most of the time and this chair will only be used to go out in once or twice a week a distance of perhaps 2-3 miles per trip which would you suggest. Please consider that it will be the wimpy 22NF batteries :lol: :lol:
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Re: Which battery do I need please?

Postby Burgerman » 22 Feb 2021, 19:39

Gel MK. Unless you like 3 month life and lack of control, and walking home. The 22nf gets murdered as its too small. So only MK gel makes sense to me. And use a charger that doesent murder them! Even the MK wont last well regardless as they are too small for the job. And get hammered. But its the best of a bad situation.

That means a charger that never exceeds 28.2V and does not charge for 8 hours or less and then stop! They need at least 16 hours charge to be fully charged. And that matters for a sensible service life. Or they will sulfate.

At some point every week you need to charge them for 24 to 48 hours. Because an overnight charge is just not adequate and causes sulfation/death long before they should really die.

And if you get a chance during the day as you eat/check mail, charge them for an hour or so. As frequently as you get chance. Daily - get into the habit. A faster charger helps get more back fast. I have many 30, 40, Amp ones dotted about. As I charge via anderson connectors. You are limited to 12A with the stock XLR connector. Although I have done 13A a lot of times with the PL8. Or direct from power supply.

To do it from a power supply like my bench ones for example, just set Amps to MAX (40A or 50A in my case) with Andersons, and volts to 28.2 for Gel. And to 29V for AGM. If using the XLR connector set this to 12A and the same volts as above. Leave it connected as long as you can while you sit at a PC or as you eat or watch TV. You MUST still do the overnight charge daily too!

Of course any battery will "work". You could just get some cheap leasure batteries. But you will be surprised how soon they fail. I did this once to try. As £50 a battery and a 3 year warranty at halfords it sounded fun. After 3 new sets in 6 months they refused to replace any more!
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Re: Which battery do I need please?

Postby LearnerDriver » 22 Feb 2021, 20:39

Based on the 22Nf being a bit wimpy I have lost 4 stones in weight and plan to shift another 2. Hopefully then at 12 stones it will mean that at least I am not completely stressing the batteries. Hey, it was a good way to convince me to shift that blubber lol

I so wish we could get away with not using the narrow base models of our chairs but we can’t.
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Re: Which battery do I need please?

Postby Burgerman » 23 Feb 2021, 00:25

Buy a :hammer cheers

All my interior and outside doors were widened so that theres 4 or 5 inches to spare on most. Front door even more. And level access. Makes life way easier.

If you are serious about using a wheelchair for the rest of your life you gotta accept that you need a bigger organised plan. And you will need to break a few eggs.

My plan cost a fortune, took me 10 yeras to pay for it. Bigger doorways was a minor part, I extended the house, downstairs by lots, and knocked down walls and made it more open plan. In a kitchen you need space. You need room to move away from cupboards and ovens and to be able to spin around all over without worrying about hitting stuff. Same in a bedroom, you need space to move, away from a bed. And doors that are 800mm wide that swing both ways (not like that!). So you can just drive into them from any direction. You need a kitchen that you can use with cupboards that pull out racking inc the high ones that pull down so you can reach.

You need low maintainance, everything. So no paintwork, All plastic. No carpets (I did the whole downstairs in large grey ceramic tiles or industrial carpet tiles.) Its easy to swap 2 or 3 tiles when they wear or you spill something which I do all the time! And wheelchairs trash carpets. They dont even touch tiles.

You need a well constructed wet room. With enough room to move! You may need carers in there too.

And a lowered floor minivan so you can drive etc. Or at least sit up front. And parking space with easy access.

Even if it means moving first because otherwise you are throwing good money at the wrong property. And the council may help wih changes. They helped me.
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Re: Which battery do I need please?

Postby LearnerDriver » 23 Feb 2021, 22:19

I hear what you are saying BM but not everybody’s circumstances are perhaps the same as yours and we are stuck with what we have and where we are.

So the narrow base model will have to do us for now.
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Re: Which battery do I need please?

Postby Burgerman » 24 Feb 2021, 00:37

Maybe. But it might pay to have a deep think about how and what will happen in the future. No point throwing good money after bad. And then figurin out later that you need to look at a much bigger long term plan. I have seen people do this repeatedly.
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Re: Which battery do I need please?

Postby LearnerDriver » 24 Feb 2021, 14:50

Hahaha don’t worry I have a raft of plans for all sorts of scenarios, just life isn’t allowing any of them to happen for us.

Ideally we would love a bungalow with wider doors, a wet room and a moat and land mines to keep people away. Ooops did I say those last 2 bits out loud.

The other bits stand, even with the option of moving somewhere else in the UK, we are as flexible as our jobs will currently allow us. Unfortunately working in school is something that we can’t do remotely at the moment....well not yet at least.
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Re: Which battery do I need please?

Postby Burgerman » 27 Feb 2021, 12:51

Well I live in a bungalow, wide doors, wet room, everything opened up, adapted entranceways, kitchen etc. That doesent mean that there isnt still 2 bedrooms and a bathroom upstairs in the roof that I have not seen for 24 years...

So knock down your neibours houses, extend around you, add space and bigger rooms etc as needed. Might even make room for your mote etc.

Seriously though, I live in a cul de cac. I have been pushing everyone in my street of maybe 30 detached houses to adopt the street. That reduces the council tax. It also means we can remove all the road/footpaths and just block pave the lot wall to wall and add a few victorian lamp posts, seats, flower bins. And have an electric BT controlled coded gate on the open end of the street making a secure area. So far only about a quarter of the residents are interested! :thumbdown: Not quite a mote but would keep all the undesirables out.
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Re: Which battery do I need please?

Postby LearnerDriver » 28 Feb 2021, 21:20

How do you adopt a street from the council, I think my neighbours would love to do that. This should have been a private road, well that’s how it was sold to us by the developers and then they let the council adopt it. It’s also a full-de-sac :thumbup:
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Re: Which battery do I need please?

Postby Burgerman » 01 Mar 2021, 00:23

Not sure. You would need a solicitor. But theres at least 4 that have been done around my area. Presumably you will need every owner to sign an agreement and go see the council! You would need planning etc presumably.
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