Part of our mission at Hanford included building a portable trunked repeater system for use in case the main and secondary site went down, or if we needed extended coverage and/or mutual aid support. We built the system on a flatbed trailer with all the goodies housed in a big poly coated steel box. We had a battery bank capable of keeping the whole system up and running for 72 hours, with a nominal power consumption 350 watts. We used deep cycle batteries as opposed to automotive type because we did not plan on running the system in a constant charge mode. We used a Marine Charger/maintainer to keep the batteries at full optimization while on standby, which was most of the time. The unit cost about $500 and was pretty smart about how to keep those batteries in prime condition. I believe Xantrex makes some of the best charger/maintainers on the market these days. Deep cycles are great for when you need to run on batteries for a long period between charges. Automotive batteries work better when you running in a constant charge mode (as with wind and solar generators, or floating the batteries on a live circuit). Deep cycles like to be fully discharged every so often, and the system we used took care of all that to keep the batteries in perfect condition.