Uh Oh where did you get the battery from? Dell's are VERY picky with batteries and AC Adapters! If they don't have the right one it either 1) Won't charge 2) Run the Laptop as Half Speed and wont charge (Inccorect AC Adapter). They do this because they had lawsuits years about with people using aftermarket AC Adapters and Batteries and the battery would actually explode and leak battery acid all over the person.
Its more expensive yes to get it from Dell. If i choose to get a non Factory item i only get it from these guys here. Comptick.com I know these guys personally and they are 10 minutes away from my office. been buying stuff from them for years and never had a single issue.
But yea unless you can tell its a Genuine Battery I'd...