How do I clean up stubborn battery contacts?

While my Canon SX150 is near the end of it's useful life due to the cost of replacement parts I need for it, I'm trying to extend it's remaining use as much as possible without purchasing new parts.

My camera has had issues with a cracked battery cover support tab (and cover) for years. That being said it has never failed me before, but even that's coming to an end. When I went to check the camera it flashed the batteries are low. I expect this condition with this problem, so ignored it. However, the camera is shutting off rather then perpetually flashing the low battery warning.

I checked my batteries (2500mAh NiMh RadioShack) and they are at 1.1V each. The batteries are fine best I can tell, so I think the problem is related to the battery contacts. The problem is I tried cleaning it with 70% IPA with more or less no effect. There is something built-up on the contacts, but it's not responding to standard rubbing alcohol. I need something stronger. Is there anything else I can use that will not damage the contacts? I'm going to take the contacts out of the camera for cleaning, so there's no concern about the electronics. The only thing I need to avoid is cleaners that are known to damage plastic, as this isn't ideal.