agm battery drained to 1.5v

Yes, just check the terminal voltage regularly to make sure it doesn't go over 15.5v, you don't want to boil it dry, but you do need to stir up the acid water mix created by the recombiners in the cells. If you don't, all the over strength acid is eating the bottom of the plates away will the water on the top gives no capacity for start up/storage, because there is no sulphur from the sulphuric acid to react with the lead and create the voltage at useable amps across the terminals .....

T1 Terry

 

Yes, in that in general neither will effectively desulfate an AGM battery. The "evidence" that any charger can desulfate an AGM battery is pretty marginal. Some chargers, like from BatteryMinder, claim that they can do so with pulses and such. I have seen people claim that these chargers really do work for them. I have not seen what I consider to be a properly controlled experiment to demonstrate desulfation of an AGM battery. Note that even the manufacturers say that the desulfation process is very slow. The battery has to be on the charger for weeks or months continuously.

Keeping an AGM battery at a high state of charge from the date of purchase will reduce the rate at which it sulfates. But preventing sulfation is a much easier task than removing the sulfation once it has formed.