From Optima's website. Not sure if this helps or not.
Both the OPTIMA Chargers Digital 400 and Digital 1200 12V Performance Battery Charger and Maintainer enhance the performance of OPTIMA and other AGM batteries, recover deeply discharged batteries and extend battery life. However, under normal vehicle-starting applications, most regular automatic lead-acid battery chargers will properly charge an OPTIMA battery. However, since OPTIMA batteries are frequently used in high-performance applications or nonstandard vehicle-starting applications, there are certain instances that must be given special considerations.
An OPTIMA battery is an AGM battery, not a gel battery or regular flooded battery. A deeply discharged OPTIMA battery (less than 10.5 volts) will not test or recharge properly if treated as a gel battery or regular flooded battery. A handheld electronic battery tester will most likely provide inaccurate results.
An OPTIMA battery has the benefit of very low internal resistance, which allows high-amperage output as well as efficient charge acceptance. This benefit also allows an OPTIMA battery to run longer than its specified ratings and run at a lower voltage than typical flooded batteries. All of this can lead to confusion when it comes to recharging a deeply discharged OPTIMA. Most basic battery chargers have a built-in function to prevent charging a battery with less than 10.5 volts. If your OPTIMA battery is discharged below that, the battery charger may not start up.
Most high-quality, modern battery chargers now have built-in features to charge AGM batteries like OPTIMA batteries. Some have specific AGM settings, which should be used to charge an OPTIMA battery. Do not use gel or gel/AGM settings, as they will not fully charge an OPTIMA battery and could damage it over time. However, even some AGM-compatible chargers will not recharge deeply discharged (less than 10.5 volts) OPTIMA batteries. In those instances, it may be necessary to follow the parallel charging instructions.
For regular charging, we recommend a maximum of 10 amps, 13.8 to 15.0 volts. For float charging, we recommend one amp maximum, 13.2 to 13.8 volts.
Under normal (engine-starting) conditions, an OPTIMA battery should never experience “at-rest” voltages below 10.5 volts. In these applications, most 12-volt chargers (old or new) or alternators will sufficiently recharge an OPTIMA battery with at least 10.5 volts. Typically, we only see issues with charging when it relates to stand-alone deep-cycling applications or severely discharged OPTIMA batteries.
These guidelines are intended for typical consumer applications. For military, commercial applications or new equipment design, please contact OPTIMA for additional technical information and assistance.
Can you trickle-charge an OPTIMA battery? And what type of charger can I use?
Yes, and you can use any charger on an OPTIMA battery as long as the voltage is regulated properly. If your charger will remain on indefinitely, the voltage should be at 13.8 volts maximum with a one-amp maximum current.
Will my high-output alternator damage the OPTIMA battery?
No, as long as the voltage is properly regulated. Because the OPTIMA battery has a very low internal resistance, it will accept high current more efficiently than conventional batteries.