SM Batteries


Our 8 x Trojan 105's 225amp 6v lead acid batteries failed here in Mauritius today after being plugged in to shore power whilst we travelled inland for 4 days. We have just purchased 8 x 220 amp 6V AGM's (just over US$2000) of same dimensions. There were limited choices available out here in the Indian Ocean and with many on the forum now moved to AGM's, we decided to part ways from the trusty Trojans we liked so much, when none were available here.

We have a Victron 24v Victron 70amp/3000w Inverter charger and 850w solar coming in through a Tracer 40amp solar controller. Our Rutland 1200 Wind Gen solar controller unit would not work with the recent 300w of extra solar panels we put on so I direct wired those in to the battery bank and that could possibly have been my downfall!

Also our Yanmar 75hp has the original standard 80amp alternator on it which I think pushes out a constant 28.8v.

Any wisdom and/or suggestions on what I should look out for or change tomorrow when I connect the AGM's into my system for the first time after running this boat on lead acid for the past 16yrs? The AGM's came with no charge settings so keen to know what most of you set your various 3 stage charge settings at?



I don't know where you are planning on getting your batteries from but I highly recommend that you check this local Annapolis place for before you buy anything:

The owner is a boater and very knowledgeable.  They have great customer service and pricing.  They have a ton of batteries in stock but they turn them over quickly.  Last year I purchased 12 x Deka Marine Master DC31DT for a lower price than I could find anywhere on the internet when factoring in shipping cost - somewhere around $120 each.  I bought them in September of 2017 and the stickers on them show that they were manufactured in July of 2017.  They also load tested each one of them for me before loading them into my car so I knew that I was not getting a "dud".  

Last, they let a friend of mine borrow some empty 6v battery cases so that he could mock up his battery bank to see how many batteries he can fit.  They would likely let you do the same if you asked.

Mark McGovern
SM #440 Cara
Deale, MD USA


Alan Leslie

Hi Colin,

There's probably little doubt that attaching the extra 300W of solar directly to your battery bank did them more harm than good. The constant 28.8V from the alternator doesn't help either if you do long periods of motoring.

Our 12 x 6V AGM batteries came with charging ranges Absorption 7.25 - 7.45V, Float 6.8 - 6.9V.
I opted for the middle of the range so for 4 in series as a 24V system, we have Absorption 29.4V and float 27.4V.
All our charging systems (Engine Alt, Solar, D400 wind, Victron 100A and Promariner 30A) are set to those voltages and all bar the D400 wind generator have a battery temperature input, so those voltages vary depending on the temperature of the batteries.

Elyse SM437