Battery 0% available plugged in, not charging

[pigeon-wing]

I'm running Windows Vista on a Gateway NX570X laptop. About a year after I bought it, it slid off the table and bent the connecter for the original AC adapter, so I bought a new adapter online. It's an off-brand adapter, but the voltage outputs and inputs are the same as my old adapter, and it charged the battery fine for about two months. Then the battery started charging halfway and then less and less until finally it reached 0% available (plugged in, not charging). Now, this still wasn't an immediate problem for me because my laptop is stationary most of the time; however, since last October the adapter has had to be plugged in at a certain angle or it won't power the laptop at all, and now it has taken to shutting off randomly or whenever the connecter is nudged. Highlights:

* Gateway NX570X laptop with Windows Vista
* Off-brand AC adapter worked for about two months before malfunctions began
* Battery life reads 0% available (plugged in, not charging)
* Adapter must be inserted into the laptop at just the right angle to turn it on
* Computer shuts down randomly, ranging between minutes, hours, and days after starting it up

I have tried:

* Removing and replacing the battery while the computer was on and off
* Reinstalling Microsoft ACPI Compliant Control Method Battery

I contacted one of Gateway's online reps about the matter, but he told me to jiggle the battery before instructing me to buy a new one (then he closed the chat). Is this definitely a battery problem? I don't have much money to spend, so I'm not sure whether to spend it on a new battery, a new AC adapter, or on taking it to a repair shop (if my small town even has a reputable computer repair shop); or whether this might be a problem with Vista.

Thanks!