Mobility scooter (gel( batteries

[Jethro_uk]

We've just inherited an Invacare Auriga mobility scooter. With dead batteries.

Checking with a meter initially, showed 0.8V each.

After about 10 minutes with a car charger, they were reading about 7V each. However the intelligent charger we have wont start charging them.

Is it worth keeping them on the car charger for a bit longer in the hope that they'll "pick up", or is this generally a Bad Thing ? I'm aware a car charger is "dumb" so won't trickle ....

Googling seems to suggest that gel batteries can't be fully charged by car chargers as they deliver slightly more than the 13V of a lead-acid battery.

[Adrian]

Depends on the charger. Some intelligent chargers have a 14.8v mode for AGM batteries. They may bill it as "winter mode".

It might be worth leaving them on the dumb charger for longer, to get them nearer to 12v, but if they've been that flat, they're probably fubar anyway.

[Tim Watts]

On Saturday 15 June 2013 17:36 Jethro_uk wrote in uk.d-i-y:

Gell batteries must not be allowed to gas - that's the main constraint I know of.

[meow2222]

Who knows. I wouldnt be optimistic. I have reconned wet cells with good res ults, but SLA are a bit different, and new ones not too expensive.

SLAs require lower charging voltage than wet batteries, so a car charger is nt a great choice.

To be honest, if you insist on messing with them I'd probably hook them up to the mains via a lightbulb and 1kV diode, with important safety precautio ns. If that doesnt desulphate them & get them up to 12v, nothing will. Once they settle to a sensible terminal voltage they should be disconnected & c harged as normal.

NT

[Dave Plowman (News)]

The chances of recovering a SLA battery which has been left flat are zero, IMHO.

[Dave Liquorice]

Or so close to zero that it's not worth trying. Especially with terminal volts down at 0.8 V to start with. Just weigh 'em in...

[meow2222]

A useful percentag of wet batteries can be recovered by rinsing them out an d refilling with fresh acid, but there are failures, safety issues, lead co mpound disposal issues, and new ones arent expensive. I expect the same cou ld be done with glass mat cells. Adding phosphoric acid can much improve pe rformance if you keep concentration within the narrow range it works in.

High voltage charging can break down sulphation, but you dont get a result like new.

Another option is new plates and new acid in the old case. I found lead roo fing sheet thats been stored and tarnished works without further treatment. But its all hassle.

Just buy a new one unless youre totally brassic.

NT

[Dave Plowman (News)]

SLA isn't wet - it uses a gel. Whether that can be replaced with new in the same way, I dunno.

[Jethro_uk]

Price I have seen for a pair of replacement batteries is £155.

As an update, overnight charging of one battery, followed by 6 hours today on the other bought both up to 12.33V ... at which point the charger seems to recognise they're present, and has started charging them.

All I really want is enough juice to show any prospective purchaser the things works. I know it does, because I swapped out the batteries from SWMBO own scooter, and it works flawlessly. We know a couple of dealers and would like to p/ex it for a "boot-scoot"

Thanks for all the info guys ... I'll file an update tomorrow, after they've had 24 hours on the intellicharger ....

[Jim.G1SSO]

I'd be surprised if a dealer give you more than 75 Jim G

[Grimly Curmudgeon]

You might be lucky but I'd not be surprised if the battery voltages come up and they have next to no capacity left in them.

[Dave Liquorice]

Is that for "mobility batteries" from a mobilty retailer or suitable voltage/capacity gel cells from say Value Power Systems?

They are UPS specialists but they've always had good prices and they may do "mobility batteries" as well.

But probably sod all capacity.

[meow2222]

There's more than one way SLAs, or more accurately VRLAs, are constructed.

1. Absorbed Glass Mat - a fibreglass mat wrap round the plates holds the electrolyte.
2. Gel cell - silica gel immobilises the acid

AGMs are cheaper & more common.

NT

[Dave Plowman (News)]

By that price, not a mobility retailer. They don't sell anything without at least two zeros.

[Dave Plowman (News)]

But can the electrolyte in a AGW be replaced? Since it is a spill proof design, I suspect not.

[meow2222]

Yes. Typically, remove the top cover and you can pull off the rubber valves and pour in acid. If you need it to continue to be spillproof, refit the valves, rotate plenty of times, and pour out any excess. Refit valves & cover.

NT