What sort of capacity do you need, you need to sort that issue out, so that you can decide how long you wish your equipment to run. You can get motorcycle batteries that are smaller, or lead acid gel cells can be made up into packs to 12 volts. For very low capacity non-rechargeable, alkaline batteries might do it, and you can buy them nearly anywhere, if they need to be rechargable, NiMH.
A car battery, or for that matter motorcycle batteries, are not intended for deep cycling, so depending on your application, you have to keep that in mind,
cheers,
Richard
