I have a Darrel Cox lithium battery that I purchased last August and yesterday it was dead, showing 6.3 volts! Wouldn’t even open the trunk. I panicked because it’s opening day at my local track today, anyway my 4 amp battery tender didn’t like the low voltage and would not charge it so I put the 6 amp charger Darrel Cox send with the battery on and it worked, it brought the voltage back up to around 12 volts and then shut off, so I switched back to the 4 amp battery tender and this time it worked, it charged the battery to about 14.6 volts and then shut off, took about two hours. Anyway everything seems good, showing 14.2 volts while driving. With a lead acid battery usually if the voltage drops below 12 it’s trash, not the case with a lithium battery.