I just talked to Zack at www.thesolar.biz
about AGM batteries, and he recommended using these 2 volt 915AH batteries hooked in series.
He explained that hooking batteries up in parallel is not as efficient.
6 of these 2 volt batteries is quite expensive at around 2K, but if I only drain to 70% or less then they should last 8-10 years.
The big + is they are maintenance free.
you can find prices for different Agm brands of batteries along with the ratings good luck