One theory might be that you need to reset the PMU. (Power-Management-Unit.)

Link to Apple's page on resetting on iBook.

I've read a lot of frustrated Mac owners online who've had defected batteries from NewerTech. Most of them dying after owning them for only a few months. Of course these were posts and mail-listings from a long time ago and may be irrelevant now.

If you bought it brand new you should definitely contact the seller/manufacture and see if you can get a new one.