if an optima falls below 10v a standard charger will read it as a dead short inside and the charger's internal protection circuits will not allow it to charge. You're reading up on optima's webpage for the info, that's a good place to start. I get customers turning in "bad" red tops all the time as cores, i started saving them and trying to charge them on an AGM charger after reading that info, i've gotten 4 perfectly good red tops out of it.