when i first got these batterys a week ago they gave me a solid 15-20 minute runs and gave me a lot of wheely torque. now i cant even pop a little wheely with them! whats the problem? should i try and take them back to radio shack? i charge them on my prophetplus charger on 4 amps and when it beeps i take it out and it gives me 5-8 minutes of run time. i dont get it! should i return and buy two new ones or just buy betetr batterys.