AGM vs. Lead-Acid

[croaker stroker]

I am pretty sure my outboard charging system was designed for Lead-Acid batteries. Can it charge AGM batteries? ...or do I need something like this Toyota upgrade??

[davidsea]

    I'm not a battery expert, but as I understand the difference in charging an AGM is in the RATE of charge, and the CUTOFF voltage.  AGMs like a higher current charge to desulfate their plates, but not a higher finishing voltage.  On the motors most of us use - 4-stroke outboards 90HP and up, with alternator/regulator charging systems, AGMs shouldn't be an issue.  The problem WILL exist with onboard or portable chargers used at home or moorage, since they're typically 10 amps or less,  and definitely with the typical trickle or maintenance chargers.   I wouldn't run them on older, smaller motors with low-output or unregulated charging.
   Most of the quality newer marine chargers will have 3 or 4 modes for the different battery types, which you select before charging.   These will provide the different voltages and current best suited for whatever type you're charging.   From what I've seen, the NOCO, ProMariner, and Schumann do, but the Guests don't. 
   I've settled on quality deep-cycle wet-cells with a permanent-mount NOCO charger in the boat.   I think that properly mounted and maintained, they're the best bang for the buck.   The 2 AGM's I had before suffered from a motor with pretty low charging current and an old-school small charger at home.   I was able to bring them back to health somewhat by using some bursts from a 50 amp commercial charger, but was unimpressed with the initial cost, hassle, and fairly short life.   If you're converting to AGM, GEL, or LIPO, I would add the cost of a really good charger into the math.   m2c   

[Yachter Yat]

   Call me old fashioned, but I'm with David.  I've always used deep-cycle wet cells. Swapped them for new every 3 or 4 years; whether needed or not, and never had a breakdown or trouble keeping them charged. Another plus is they were always less expensive.   I don't know who actually made them, but Sears Die Hard Marine/RV was my favorite. 

Yat

[davidsea]

Call me old fashioned, but I'm with David. 

Yat

Well, OK, if you insist..............you're old fashioned.   

[Yachter Yat]

   Yes! And as I'm sure you're probably aware; there are times when being "old fashioned" works best.   

Yat