12v GEL battery charging

[Stumpjumper]

Hi all, I have a 12v gel battery from a mates wheelchair (no hes still mobile) I dont want to damage the battery but I need to charge it, is it ok to charge from the car? What I have been doing to charge is use one of those small solarpanels 4W rated and i leave it charging out in the sun. I have googled gel battery charging Too much info but not specific, and ended up feeling confused. I would like to charge it with the car and also maybe my 240/12v battery charger......
Iknow a lot of you out there must be using gel batteries let me know your ideas.

[YNOT]

To get the best performance and life from a gel battery you need to use chargers that have gel compatible algorithm. Next best is a multistage smart charger like a CTEK or Redarc. Don't use one of those $20 arlec type unregulated chargers.

Tony

[the evil twin]

I Use 'em by the pallet load for work... and pretty much agree with Tony.

Being gel allows them to accept a slightly higher charging voltage over the standard gassing voltage of 14.4 which translates into faster recharge amongst other small advantages. They will still charge up OK on a standard charger (with "standard" equating to Tony's 'not one of those $20 jobbies').

[Stumpjumper]

CTEK D250S Dual DC to DC Solar 12 volt Battery Charger AGM DEEP CYCLE CARAVAN,
*12 Volt Smart Pulse Trickle Battery Charger

I found these two units on ebay, the first will handle altenator and solar panel. The second is a 240v charger for GEL; AGM and SEALED batteries. Anybody used either of these and can give me an opinion marty

http://www.ebay.com.au/itm/12-Volt-Smart-Pulse-Trickle-Battery-Charger-NEW-/120799027174?pt=AU_Motorcycle_Parts_Accessories&hash=item1c202edfe6

http://www.ebay.com.au/itm/CTEK-D250S-Dual-DC-DC-Solar-12-volt-Battery-Charger-AGM-DEEP-CYCLE-CARAVAN-/320781970519?pt=AU_Car_Parts_Accessories&hash=item4ab0186c57

[CptClinac]

Hi guys,
I've also done quite a bit with gel batts. I disagree with Evil Twin regarding charge voltage.
The slightly different chemistry of the gel battery shold not be charged to the same max voltage. In Pb-Acid batts this is 13.4 through to 14.4 V absolute max. In gel this should be reduced to 13.2 to 13.6 V.
Most cheapo chargers allow the battery to overcharge at 'trickle' (up to 16V at very low current) where gasing will happen. Not too much prob as water can be replaced. On sealed batteries this IS a problem. On gel batteries this is even more of a problem.

If your car alternator is set to definitely no more than 13.6 V you can connect it OK. Watch out for excess charge current heating the battery. (ie don't try putting a small gell cell on a 150A alternator).

A cunning ploy to charge the gel from a slightly higher V alternator is to fit a silicon diode of sufficient current rating in series. Each diode drops aprox 0.6V. You can pick 10A diodes from Jaycar etc. This would allow a 14.2V system to be used to supply 13.6max.

Bare solar chargers are much the same as the cheapo chargers. I have put a regulator on my solar-gel system.
My solar charger claims to be suitable for automotive top-up and has a max V of around 18V ! ! ! ! !