new batteries

[DREW]

I tried to do a search here, but the term batteries came back as too general. My issue is this: I want to replace my stock, crappy batteries,U1 sealed lead acid batteries, with better batteries (better range) that will NOT involve major changes to the charger or stock wiring. I am aware of the brands recommended by this board, but I’m not in the position to buy the best gel batteries and pay for a ton of modifications. Just the next step up would be fine. Thanks. I live in the US.

[JoeC]

Could you fit any batteries in the chair that are physically larger than U1?

[Burgerman]

The reason JoeC asks this is because a powerchair or any electric vehicle is totally limited by its weakest bit. The batteries...

So if you already have batteries that fill the battery compartment then you are basically screwed without moving to a chair which is physically bigger. To fit in bigger batteries. But this too is limiting, because the batteries are heavy, so any gains become smaller and smaller.

The only REAL option is to move to lithium batteries like the rest of the world did years ago. Its why your laptop, phone, electric bike, full size electric car etc doesent use lead. So while its possible to move to lithium, it isnt a simple plug and play option. But it would allow around 2.5 to 3x the range that you have now.

My new chair uses lithium cells for exactly the same reasons.

http://www.wheelchairdriver.com/BM-MK3- ... rchair.htm

[JoeC]

I'm sure he understands that, but if he's concerned about the cost of MK gels and re-wiring, then lithium isn't much of an option.

With the peukert effect, size U1 batteries are *severely* limited. Even moving to group 22 size would be a major improvement. Moving to group 24 (even with something cheaper than MK) should be even better than that. Just adding larger MK gels would be a big improvement over what he has now, and would be OK with existing wiring and (probably) the charger that came with the chair.

[Burgerman]

Agreed. But normally the biggest batteries are already installed in the space available. If he can get bigger ones in then that would be great.

What chair are we talking about?

[DREW]

The chair is a Merits P326A. i''m not sure if larger batteries will fit or not, but I'm thinking not as I don't recall seeing any padding or spacers around the batteries. Thanks for the info. I'm guessing MK or Odessey is the way to go in replacing the crap thats in there now. Thanks again.

[Burgerman]

Yes, but you still will not gain much unless you fit more Ah than you take out. Unless they are severely knackered...

[JoeC]

I wouldn't put Odyssey in that chair unless you can commit to getting a rapid charger, and doing the wiring to make that work right. The Odyssey batteries would be able to keep the chair driving until they are well and truly dead, and if you did this to them often then they would quickly die. You're less likely to kill the batteries in a matter of weeks if you use the MK, since the chair will start to get sluggish an warn you that they're empty.

I wish I could recommend something that would actually give substantial improvement over what's in the chair now, but without a better charger and wiring, the Odysseys just won't live long.

[Burgerman]

http://meritshealth.com/02_products/pro ... =36&ID=276

Should anyone want to see.

Its really an indoor chair so theres not a lot you can do. And while they claim a nice round 20 mile range, I frankly doubt that you would get half that in real world conditions.

[DREW]

It's very nice indoor places, the store, etc., but the range has suddenly dropped. It certainly had more battery life when I got it 7 months ago. Now even the shortest trip on smooth, blacktop, trails, drains the battery within five miles or a little over an hour of use. I have barely made it home on two occasions, with the battery indicator seriously in the red (very low) and very limited power. I have never seen a battery discharge so quickly without a problem in the charging system (on bikes and cars anyway)
Can someone please tell me that this is normal or not. I understand that batteries lose their power over time and use. However, these batteries seem to be discharging too quickly.

[JoeC]

It does sound normal for such small batteries to need replacement after seven months if they're used daily, especially if they're run down very far.

Two things harm lead acid batteries- discharging them at high rates, and (much more so) deeply discharging them. A deep discharge battery might be good for 200 to 300 discharges at 80% depth of discharge, or more than double that if you only discharge it 50%. A starter battery (as from a car) might only last for dozens of cycles when discharged deeply. A high quality deep discharge battery that is rated for 80% depth of discharge in the 200-300 cycle range can last thousands of cycles if it's discharged less deeply. This is why Burgerman's been able to keep is Odysseys at peak performance for multiple years when he used to destroy batteries in well under a year. He uses a rapid charger to top them up frequently and keep their average depth of discharge very low.

The U1 size batteries have two strikes against them- they have a high effective rate of discharge (pulling 80 amps out of a 30AH battery is a bigger deal than out of a 60AH battery), and just driving around during the day discharges them to a much lower percentage of capacity remaining, so they'll die faster. Unfortunately that's just the reality of wheelchair batteries.