Charging An AGM Battery...?

[Seafever]

I think the charger on my Merc Outboard limits out at 15 volts....I use an AGM battery (Absorbent Glass Mat). I saw on the net you are never supposed to use a charger that goes over 14.4 volts or it will damage an AGM. And never supposed to use an old non-current-limiting automotive charger. My battery I bought from CanTire in 2007 and it is still going good (Nautilus Spiral Cell)....but that's 6 years and I fear it may die from old age. I have used it last year on my current Merc and it seems to be o.k. so far........holds a charge when stored for months..... Was just wondering if the onboard Merc charger will eventually kill it because it's a tad higher than recommendation? I like the AGM type batteries because they resist boat vibration so well....I don't get very long life out of any marine wetcell battery. No outboard-engine built-in chargers go below 15 volt max as far as I know.

 

[GabriolaJohn]

My Merc 235 never charges over 13.5 on the meter

 

[Seafever]

How fortunate thou art,my friend.....I think mine will peak at 15.....

 

[trendsetter]

Most outboards have fully regulated charge output and peak at 14.6v while the battery is charging and hold at 13.6v when the battery is full. If your merc is charging to 15v it's probably got an unregulated rectifier (common in pre-1986 outboards).

If you are not noticing any problems with the current battery I wouldn't worry too much about it. 6 years is a good run for a marine battery and you may consider replacing it for piece of mind and to have a warranty once again.