You may have heard myself praise Nokia's 'hero' battery, the Lithium-Polymer BP-4L, rated at 1500mAh, and used in everything from the E61 to the E90, most Eseries devices seem to be based on it, plus it's the core of the likes of the 6650 and N97. Anyway, it turns out that David Gilson (of this parish) reviewed a third party 'drop in' (i.e. no new phone back needed) replacement for the BP-4L, rated at 1900mAh, back at the end of 2009. Having updated it with new information (it works properly in the N97, but didn't in the original phone), I thought you'd be interested in having a read too.