I haven't used my Vex for maybe 2 years. My battery's voltage had dropped to I believe to around 6-8 volts. I charged the battery for a few days. It was charging around 13.5v, pulled it off the charge and I think it was around 12 volts but dropped to 11.49 in about 24 hours and to 10.91 after maybe a week. Should it be holding voltage for a longer period than this? Could it be time for a new battery? This one is atleast 5 years old.