After allot of checking and testing I found out the following: Passenger battery is good. 12.63 volts after charge, hydrometer readings almost identical across all six cells. Driver battery bad. 11.6 volts after charge, hydrometer five cells about the same, one cell completely dead. both batteries together read about 12.2 when trying to start the truck voltage drops to 8.9 truck will start, but struggles to do so. Batteries are three, or five years old diehard golds. Second set of diehards in the last seven years. Will not buy them again. What I really want to know is do I have to replace both batteries? Could I get away with just replacing the driver battery? I know I should, but times are tight at this time. Thanks for any and all help.