Ironman 65L dual compartment Fridge / Freezer

[Cuppa]

AGM's are lead acid, they just have the electrolyte suspended in glass mat (Absorbed Glass Mat) instead of in liquid form. That charger would charge the AGM ok, but because it is not a smart charger it would be possible to overcharge the battery, consequently you would ideally need to know the battery's SoC & the output of the charger to know how long to leave them hooked up together. In reality the battery will reduce the amount of charge it will accept as it gets 'fuller' so overcharging is probably only a possibility if left hooked up for long periods. Leaving it on charge for a few hours should be fine. Best to leave it on for two or three hours, disconnect & let the battery sit for half an hour. Connect a small load to the battery (e.g., a 5 watt globe or similar) for 5 minutes, disconnect it & let the battery sit for another 15 minutes or so, & then check the voltage across it's terminals. This should then give you an idea of it's state of charge & you can decide whether to repeat the charging process. If after checking like this you get a reading of 12.7v+ you can consider the battery well charged.

Cuppa

EDIT. If the charger is intended for batteries of 10 to 60 amp hours capacity, it will still charge a 120 amp hour battery but will take longer. In the unlikely event that the charger were a smart charger, it would still be wise to disconnect & check as I have suggested as it is possible for an undersized smart charger to overcharge a battery bigger than it is intended to be used for.