If you are genuinely using 'truck' batteries then they will quickly die as they dont do many 'cycles' ....the leisure batteries that caravan/boat people use are the type to get as they can stand an awful lot more discharges. A cheap substitute are electric truck batteries...the 'ride on' pallet truck items.
Also, Maplin do an excellent little solar set up for £200 that will drive this type of set up.....I used to use 3 x 120amp/hr batteries on one of these and during the day I ended up with close to 17v that dropped back to 14v  as they settled back.
http://www.maplin.co.uk/60w-solar-power-kit-223250
The little control box is very good and has a USB and a 'car style 12v plug' thats dead handy for phone chargers