I have seen new batteries that are bad. bad batteries can cause alot of issues…also check your keyboard, mouse and other hardware to make sure the cords are fully plugged in.
Ususlly when the “F1 to continue Del to enter setup” comes up the bios has detected a change in something like the keyboard(could be a stuck key), mouse, the amount of ram lowered,time settings, and a few other odd things.
I dunno, it sounds like it’s the battery, and as EvoTicTak pointed out, batteries (and other things) can go bad quickly. Just your luck I guess. I’d try a new battery to eliminate that as the problem.