Evo 3D phone restart battery problem

lately when I restart my phone my my battery drops 20%. I am restarting the phone at 100% and it is charging but every time I restart the phone I lose 20% battery. Think it's time for a new battery ? I know it's time for a new phone lol, 3 more months and then I can upgrade

I've had that problem too, I have enjoyed my time with this phone but I really can't wait to upgrade either.