Sidekick 4g charging problems

[Matthew Shane Ganey]

I have a sidekick 4g unlocked on at&t that I got from my brother a couple years ago, and aside from random shutdowns and a touch screen that doesnt react well to any amount of humidity its been a pretty good phone... til now. It started the other day when I plugged my phone up to charge and it didnt acknowledge the charger being plugged in at all, no charge screen, turned on or off. But the weird part is that it had about 4% left when I plugged it in and when I woke up the next day it was fully charged, but still no charge screen. When I looked at the battery status in the About Phone tab in settings, it said "not charging" with the charger connected. Any ideas? Ive been told its the battery by my sister in law who actually used the phone before me, as she said she had the same problem. But I would think if the battery is dead then the phone would recognize the charger, just that the battery wouldnt hold charge.