1 pointI've had batteries act as yours and sounds like it had a bad cell; at full charge it would seem to be okay, then quickly lose the cell and fail to start vehicle. I think your start problem will be corrected (with the new battery). p.s. This can even occur with a fairly new battery. I just had the same (or very similar) problem with a six month old motorcycle battery that just wouldn't hold charge in one of the cells.