If an OPTIMA is deeply discharged (below 10.5 volts) most basic chargers will not supply a charge.

 Also keep in mind an OPTIMA will not recharge properly if treated as a regular flooded or gel battery.

To charge the battery, you can wire a second fully charged automotive battery (12+V) to the discharged AGM in parallel (+ to + and – to –).

Then hook up the charger to either battery, setting the charger at 10 amps.

 Leave for two hours, monitoring frequently.

During this process if the discharged battery gets very hot or if it is venting (hissing sound from vents) then stop this process immediately.

When the discharged battery reaches 10.5 volts or more, remove the standard battery and continue charging the AGM until fully charged.

For normal charging a relatively low current, such as one or two amps can work well, but when the battery has been deeply discharged, some sulfation of the battery plates may have occurred. If you charge at 10 amps, the higher current will help to break up this sulfation.

If you have an automatic charger, let it run until the charger indicates charging is complete.

 If you have a manual charger, you can get a rough estimate of the charging time in hours of a completely discharged battery (11.2V) by multiplying the capacity (amp hours or Ah) of the battery by 1.2.

If your battery is not completely discharged the time would be less.

In most cases these steps will recover the AGM battery.

It’s okay for the AGM battery to get slightly warm during the charging process.

If it’s hot to the touch it means there’s a short and the process should be discontinued.