I also use a motorcycle battery from Sears, works great and lasts quite awhile even with occasional night use using running lights.

:: I'm not an electrical expert, I use two garden tractor
:: size 12 v batteries- 5"x7"x6"high. I assume to get
:: lighter I could use one smaller battery- What size and
:: spec does any one use just to run speed/depth instuments
:: for the day