Hi Steve

A Cetek XS 3600 charger (about £50) may well rescue your battery for you. The battery I believe is an Odyssey PC925 and would be well over £130 to buy so this is worth trying. Most gel batteries (for example those in golf trolleys, alarms etc) don't like being fully discharged but these Odyssey batteries are designed for deep discharge low maintenance use such as boats and caravans. The Cetek XS 3600 charger (NB not the cheaper one) is clever enough to recognise a deeply discharged battery and charge it accordingly, though it may take 48 hours or more in the first case, and several weeks on standby charge to fully regenerate.

When I bought my 4/4 the battery wasn't great - it had been in storage by the previous owner for a year then charged up just before sale by the dealer. I thought I'd have to replace it as the voltage would drop more than it should under load (lights etc) down to under 12v. However the Cetek rescued it and 2 years later it happily goes weeks without a charge (if I forget to connect the charger or if I go on holiday), it cranks beautifully and voltage drop under load is minimal.

If you're going to use the cig lighter, check it works first (mine wasn't connected!) and also that it works when the ignition is OFF (it should be wired direct to the battery, via a fuse - but some are wired via the ignition switch in the same way as a radio). Recently I replaced the original "el cheapo" socket with a marine one (Sutars) which for a few quid gives a much more secure connection and has a rubber cap to prevent shorts from objects in your glove box. I'm happy to charge via the lighter socket and have done for over 2 years now.

The cetek comes with a quick-disconnect umbilical cable which you can wire direct to the battery - note the cig lighter plug is an extra. As your battery is under the seat you can unscrew the parcel shelf, fit the cable and bring it out so that it's accessible in the back of the car, tucked under a carpet, if you like. I didn't do that because my battery is under the bonnet.

Do you know how long it has been flat? Presumably not when you bought the car?

Good luck - try the Cetek first

Nigel