Power for an outdoor project

[Foster]

I'm working on an electronic bench (lights, sounds, etc.) that will be outside. Going in position was there would be an outlet. No go, so it's battery power. Solar charging was an option, but after looking at the location, sunlight hours, etc. it's a non starter.

I'm now looking at using the battery packs for portable drills/saws/etc. One pack will run the unit for a few days (depending on use, etc.) Plan A is to hit the local flea market and buy a defunct drill, take it apart and harvest the battery connection. I'd mount it under the bench, most likely so the battery hangs down to keep rain/snow/birds /etc. from filling the cavity.

I'd pick up a pair of battery packs and a charger (one on the bench, one on the charger) to allow for a busy day of use.

Peak load is about 2.5 amps and that's only for 500ms to do full on all three RGB LED's as a quick surprise flash. Normal load would be ~1 amp with a 20% duty cycle. So I'm expecting a full day use, but there is the second battery pack.

Flaws in my plan? Tips for mounting the battery holder on the bench?

Thanks!