Speaker turns itself off seconds after being turned on.

so here's what i know.

1. the speaker turns itself off after being turned on.
it shows a full battery (5 white leds), beeps the "bluetooth connection beep" twice, then turns off with the shutoff sound
2. when connected to the charger, it doesn't turn on at all
3. suspected a swollen battery, but the battery seems completely fine visually
4. removed the 2 big speakers to visually inspect the main board, couldn't notice anything out of the ordinary, no burnt traces, no swollen capacitors or anything
5. last ditch effort, tried plugging the charger in with battery removed, no response at all

the speaker is about 3 years old, 1 year out of warranty and functioned perfectly until one day it just wouldn't turn on.
I don't have access to a multimeter, but if that would help, I could borrow one