I used to use the Schumacher 1.5amp maintainer in my E53 engine bay and recently upgraded to this 4 amp unit from Harbor Freight for use on my H8 size AGM battery
https://www.harborfreight.com/4-amp-...ner-63350.html
Been using it for months and have all my BMW vehicles on them now and have experienced no issues. This unit has a specific setting for AGM batteries (as well as lead acid) and a winter setting which is user selectable.
In the E53 engine bay, the unit fits nicely on the driver side (US) just ahead of the shock tower. This allows easy connection to the jumper terminals and electrical power out the front of the hood.
Mike