I bought a battery from eBay merchant imetroshop in Hong Kong. It was advertised as a BP-4L, turned out to be a counterfeit, and the only part of it that was decently made was the bogus label and hologram. The contacts didn't fit until I rebent them, and the battery only took half a charge. The seller refunded all my money including return postage.

I then bought an inexpensive battery from a mail order seller here in the San Francisco area. It was marked 1200 mAh, and performs as advertised. But when my main battery died, I bought another genuine Nokia.

Had I seen this post first, I would have bought the higher capacity battery from Mugen and given it a try.