AGMs and standard alternators

[olson34]

This thread started out with a discussion of using AGM's and alternators.
Then the thread changed direction somewhat with the pluses and minuses of AGM chemistry.

One feature that several posters allude to is selecting the most appropriate type of battery chemistry for the need.
About a decade ago we followed the lead of a friend of mine that added a second bank to his 33 foot sailboat. He could not find a location where a flooded battery could be accessed for servicing, so he added an AGM spiralcell battery in a custom mounting under a quarter berth. I had a similar situation in our boat, and had nowhere to add a second bank where I could get at it.

I also built an frp box for a spiralcell battery for starting/emergency use and housed it under a quarterberth.
Both of our boats have flooded "house banks" and we seem to be getting by for a decade with no particular problems.

My house bank is a pair of Trojan T-145's.

I had been charging the AGM once every month or three by switching over to that bank for a while while motoring. What with that battery technology having so little self-discharge, that battery seems quite happy that way.
I start the three cylinder diesel on it several times a year just to verify its condition.

A very recent change/upgrade in shore power chargers has me wondering if this is finally the time to safely leave the charger on float for both banks... I never used to do this because the old charger had no setting for "AGM." The new one, a model 1220i ProTech from ProMariner, has switchable charge/float settings for all three battery chemistries.

After doing a lot of research, it appears that I can nowadays leave the setting on AGM and not harm either bank. This does slightly lower the float voltage, though.

Our engine uses the stock Moto 50 amp alternator, rebuilt as needed over the decades, and working fine.

Is this setup going to continue to function OK?
What say ye, DC Gurus?


Thank you,
L

[mitiempo]

I'm not sure of your charger's voltage settings for the different types of batteries but the Xantrex Truecharge2 is very close for AGM and flooded. Absorption is 14.4 flooded and 14.3 AGM. float is 13.5 flooded and 13.4 AGM. The accuracy is .1 volts plus or minus. I would think either setting on this charger would be ok for both AGM and flooded but somebody may have another opinion. And your charger may have different voltages for each type.

From the Xantrex manual.

[roline]

I installed 2 banks of AGM batteries over 6 yrs ago with the original 35 amp alternator on a 2GM20. Over the yrs, the only thing that has changed is the alternator, first a 55 amp and last yr I found an 80 amp for under $100. Folks can argue both sides, but Im a firm believer that AGMs are the way to go, $tiff up front, but worth it in the long haul. Another boat owner in our marina learned the lesson that flooded batteries don't work so well when submerged. After we pumped him out he replaced his water logged batteries with AGMs. He learned the lesson that AGMs have an important advantage, especially in an emergency situation.