Inkpad Color freezes, new battery needed?

I seem to have a similar issue on my Inkpad Color as described on Inkpad 3 in this and this thread. The whole device just dies on heavy screen refresh, especially if colors are included. Everything works fine on charger. On battery, I can read text books for a time but eventually if left on or in sleep mode it'll crash and freeze even though battery is almost full and requires reboot while connected to a charger. Also it seems the battery is draining quite fast while it's in thise frozen state, so I suppose it's not actually shut down. I tried doing factory reset but it did nothing.

Unless anyone has any other ideas, in hopes it'll give me a few more years, I'd like to find a replacement battery, which as of now I've not found yet, so any tips on that would also be appreciated.