best thing you can get is a CYCLON pack.
These are individual 2V cells that do not self discharge over time and are capable of very high discharge & recharge rates.
You should see a lot of them on the used market as they are standard fitment in all portable gear used in airports and it is manditory ( down here any way ) to replace thes batteries at set hours which are about 1/3 way through the life span.
Otherwise google them .
They sell them prewired in packs for 6V 12V 18V 24V 32V & 50V