The batteries definitely sound like they're no good. If you're looking for the high capacity batteries as replacement, consider:
- extra size and bulk
- need for new case (if you use one)
- availability of battery door (although most sellers will include the appropriate door with the battery)
- your use of the device (if you're going to be near a power source, you may not need such a mega battery)
If you want a bit more capacity in a smaller form, consider the 1800MAH EXTENDED BATTERY by Mugen. It's just a few millimetres thicker than the stock battery, but gives you a bit more juice.
Also, take a look at this thread that is currently discussing aftermarket batteries:
Battery Recommendation