I have a Gel 8 ah that I bought off of ebay: http://www.ebay.com/itm/UPG-12V-8Ah-UPS
$18.99 delivered to the house - free shipping and no tax.
I have a Gel 10 ah, and not an 8 ah. Bought it from the same place as in the link.
Battery measures 5-7/8"x2-1/2"x4-1/2" high. (Figured you might want to measure
your back hatch and relieve your worries about whether or not it will fit.) If you decide to
go with the 8 ah, then battery naturally would be a little smaller. I think mine cost $19+change - not much more. I jumped the gun on the original price by looking at the link
and thinking that I had the 8 ah. Should have checked before posting original message
S o r r y !
Charge same with 1.5 amp charger. Takes about 10 hours to get full charge. But that's after I have run the battery down for the whole weekend. Charging time for daily use would be much less.