Not really CHDK related, but i thought i might as well report it here since some people come looking for CHDK to solve it. There is a known problem with a part of the SX280 / 270 model cameras that makes them shut off (long) before the battery gets empty. For some it is only during video recording, but for me at least, it happened in any mode, making the camera basically unusable until i learned to tape off the middle terminal of the battery. This seems to be a hardware problem that cannot be solved in firmware or with firmware extensions like CHDK. Canon, at least here in Europe, is now offering free repairs on cameras with this problem.