How long can a battery pack sit?

Just pulled the front cover off it just takes a second and put your meter on it It's going to be around 200 volts I bet depends I didn't even look to see where you're located but if it hasn't seriously frozen should be in good shape and it's already out so there's no reason you can't put a trickle charge on it 300 volts at about 2.4 amps it'll charge right up to about 240 50 60 volt somewhere in there and then it'll stop changing on the meter and you just disconnect the charger Don't let it heat up

 

The new battery is better than the old one.
The battery will be charged from the hybrid system. There is no need to make unnecessary movements.
You can take readings with the program and post the photo in Priuschat

 

First is it brand new from Toyota or “new” reconditioned from one of a dozen companies including Dorman at the local auto supply? If not new oem, it’s used with some modules swapped out. Even if it has a shiney Dorman paint job. Worse yet if it’s a lithium or cylindrical NiMH aftermarket replacement.

If it is new oem or used and has discharged itself, which that is likely, it won’t start the engine. Without the engine you can’t force charge it.

Tom is anticipating that scenario and suggests advanced battery teardown and charging with a special charger you buy. Even then some modules may be bad requiring a total disassembly and individual module replacement which are only available used. Overall a risk. If you paid $500 it might be worth the risk.