I recently started playing with my 2 Traxxas Slash trucks again, since winter and other projects consumed my time after last summer, and now my 8.4 volt 7 cell batteries won't fully charge up from my EZ Peak 2 amp charger. Do I need to toss my batteries and get new ones or can I drain them down and stay over? I have 6 3000mah series 3 and one 4200mah series 4 battery. Any help would be great as I don't really want to have to buy new batteries unless I absolutely have to. Thanks!!