MY first post wooho lol

hello everyone
I am new here, well i been reading for 4 day trying to learn everything i can
about the Toyota Prius
my only experience with this car was a few years ago,taking a battery from the salvage yard in pieces to build a 14.4 battery for car audio the project it work.

now i was going to do it again and found a 2001 Prius for sale on ebay
its been crash at front hard right side, the owner of the car got both new batteries and inverter replace at the dealer last year they look new i was going to take them out but i have decide to try to repair this car the damage is on the right side very close to the engine , the metal was pull radiators and fans are destroy and the rear right axle came of from the engine and the fuse box got a little damage but i can fix the 2 cables that are damage and replace the singe broken relay

also there is a dent on the top part of the inverter so i opened it and it was near the capacitor and there is no damage
my question is this
how can i prevent the big battery to die ?
12 volt battery die at the towing company right now it is charging with fully regulated 3 amp power supply

what can i check before i power on the vehicle again, i just want to make sure the hybrid parts are ok
and i don't want to waste a lot of money fixing it and later find something bad that will cost a lot
thank you for all your comments help