Had ongoing issues with my XT910. It was sent away 2 months ago for repairs as the battery was going flat very quickly. The battery was replaced (they claim) and its all good (they also claim). Yet it still only lasts barely 10 hours on standby even in flight mode (sim and memory card removed) with no apps running. The other night I switched it off when it had 40% battery life left, in the morning it was completely flat Is this a classic sign of a defective battery or something more sinister?