I see thanks for the info. can I ask how it messes things up, what is misread? I can understand that the percentage can be wrong if it assumes the wrong maximum charge based on a previous battery but surely this should not have this effect on the rate at which it loses charge. zero will still be zero and anything inbetween should just be the same, right? even if we assume that the battery drains faster shouldn't the second derivative still be almost the same? why does it drop like this? Gabby Just to be clear it rapidly hit zero before I changed my battery, not during the change. it didn't take me an hour to change it :P