Surely a great big heavy battery would cause more potential problems than dropper drilling?
It’s the flex in the tube in the area of the hole that causes failures, prob more than what the hole is for / carrying etc. There’s a lot of strain in the lower seat tube area and not much on the upper DT area. Metal tubes with holes in certain areas need thicker walls to pass tests than non-holed tubes and it’s one reason I dislike internal cable routing in general. I assume you’re talking abut a drilled metal frame, not CF 🙂
Unless you’ve seen stress/strain FEA for the frame under pedal and impact loads I’d be wary of a home-drilled frame tbh. No warranty and a lottery on lifespan. Even brands get guide placements wrong, look at how many Ti frames with internal routing guides have cracked as an example.