Inspiron 9300 - Strange Battery/AC problem?

Hey, I'm wondering if anybody here has had a similar error with their machine. My Inspiron 9300 is acting strangely - it no longer seems to recognize when it's on AC power. Instead, when the AC is plugged in, the computer states that it's on battery, but with hundreds of hours left. (Currently 525 hours at 60%.) The battery doesn't seem to be recharging at all, and is very slowly dwindling (very quickly if I take the AC out). It also did not recharge at all when it was on standby or hibernate. I'm going to power it down and clean the battery contacts after this post, but has anybody heard of similar errors?

Possible relevant notes:
The battery IS 2-3 years old, but was holding at least a minimal charge last week.
The computer recently suffered another battery/power issue, where it would start flickering between AC and battery power (visible through screen changing brightness levels). It would start as microsecond flickers, and gradually deteriorate until the AC was no longer recognized at all. However, replacing the AC adapter seemed to get rid of this problem entirely.

Thanks in advance!

Update: No charge while turned off. Refused to start off of AC power without battery.

 

Bumping for assistance. My current best guess is a loose connection on the motherboard. If that's the case, any guesses at repair cost?