The problem with batterys is that they can give afalsevoltagereading after charge (surface charge) that can make a bad battery seem good.
You can take a battery that has charged overnight and load test with a battery checkerbefore a first flightand may be led into a false security that the battery is goodas the surface charge of the battery will give you a good reading, however if you load the battery for a period (five minutes wiggling the sticks) to remove surface charge then the loaded battery checker will give a true reading of the battery capacity.

The surface charge is "the false peak".