The battery life of my Skate has worried me ever since I got the phone. It was nice and slim, but needed battery swaps or charging multiple times a day for constant texting and surfing on EDGE and Wi-Fi. I checked online for extended batteries that would save me from the hassle, but I couldn't find any.
Recently I had some time to extend my spare battery (bought from eBay for USD4.50 which originally had half the capacity of the stock battery) with with a genuine Nokia BL-5C. The battery life improved substantially, but I still wasn't happy with the 4+ hour screen time (0% brightness all the time). Last night I added a second BL-5C cell to the pack, which made the phone look much like a banana with my silicone case on, but it doesn't feel too bad in the hand, at least for me. With 13 hours since boot, over 6 hours of screen (half of it 40, and the other 0%) time and Wi-Fi always on, I've managed to kick the battery level down to 14%.
I'll post a few pictures of my power plant tomorrow, in case anyone's interested.
PS. There's a lot to improve (eg using an OEM battery as the main cell to improve capacity even more, modifying a silicone or hard case for a better fit etc).