I don't know how old the battery is but it is a Kirkland Signature - Costco battery, so I know it is not original. The voltage before I start the truck is 12.2 volts. After starting the voltage jumps to 14.5 volts. Within a minute the voltage lowered to 12.9 volts and I have measured it as low as 12.5 volts while the engine is running. I notice that the volt meter on the dash will go up and down while driving. I noticed that the vdc off and slip light illuminated while at the lower reading but does not go off when the voltage rises.