Recently my Mercury 115 2 Stroke Outboard Motor shut down while out on the water, fortunately not far from the ramp and trailer. No fire to any of the four plugs. At home, further testing revealed the stator had went bad. Replaced with a superior stator made by CDI, and also replaced the rectifier/voltage regulator with a CDI Rectifier. Now runs better than it has in a long, long time (1992 model).
On the installation sheet, it plainly states: " DO NOT USE A MAINTAINENCE FREE, AGM OR DRY CELL BATTERIES AS THE USE OF THESE TYPE BATTERIESCOULD VOID THE WARRANTY AND DAMAGE THE REGULATOR/RECTIFIER AND OR THE STATOR!!!".
I do not use AGM batteries in my boat, but just wanted to pass this along to those who do.
Here are the sheets to review yourself. This may or may not apply to newer model engines, but is something to know about. Before considering use of an AGM battery in your boat, it may be worth your time to check things out.

http://www.cdielectronics.com/wp-adm...S-194-5279.pdf