You should use the same battery tie down to secure it or get something from an auto store, a bungie strap, cargo strap, etc. THe battery shouldnt just sit, lay, hop, jump or vibrate in its spot.
Yes, you can use a range of 12 volt batteries, most stores in America sell tons of small equipment batteries for motorcycles, atvs, jet skis, mopeds, etc. The group 51 is the biggest a few of the US owners have used with no problems and improved ima performance.
Fully Eco Modded 2010 Honda Insight PHEV
Semi Eco Modded 1995 Suzuki Sidekick LJX