quattro Digest, Vol 35, Issue 50

[thejimrose]

speaking from 5+ years in the car audio world, i've had good luck with
optima's red top bateries and have had them in several cars. ive gotten good
life [5 years on 1]  and very few issues with them.

i had one in my 5000 for a while under the back seat, and never had any
issues with it as far as gassing, working on the assumption that it was
'sealed'.

altho.. i'm probably going to get an odyssey for my next batt in the a4.
theyre incredibly well made and much smaller and lighter that a normal
battery. ive spoken to a few folks that have had good luck with the pc680
motorcycle battery in the a4's. once guy in MN.

http://www.odysseybatteries.com/

you can mount them any way, upside down, etc. they're deep cycle, 3 year
warranty and a 10 year lifespan. plus they specifically say can be mounted
in the pass compt.

theyre also generally regarded in the motorcycle world as the best battery
out there. no affiliation, etc. just impressve product.

cheers
jim