AGM batteries with the A4?

[Tommy jones]

Has anyone used AGM batteries with their A4?
I have an extra new one from another boat that I was thinking of swapping into the sailboat. I am a little worried that the A4 alternator will over charge the AGM and destroy it. If I am better off leaving my flooded batteries in there I will.

Thanks for any insight.

[roadnsky]

I have AGMs. One of them is 9 yrs old.
No issue with my ALT setup charging them over that time.
But...

Would you be "mixing" the AGM with a flooded cell?
What alternator is on your A4?
Do you use a battery charger? Multi stage?

The answers to those questions will all play a factor.

[TomG]

When I got my current boat (with an A-4), I had to get new batteries as the original lead acid were shot. That was in November 2010. I installed a matched pair of Group 24 AGM batteries, a Blue Sea SI ACR, and a 55A alternator from our host here. I've never had a battery issue. (Knock on wood). Some folks like more control of their battery states, but the way I use my boat, simple works best for me.

I would NOT mix a lead acid with an AGM, without sophisticated charging control and monitoring system.

[Tommy jones]

i would not be mixing the batteries. I will be subbing out AGMs for the ones i currently have. I already have one new AGM, so i thought this would be the time.
I have a hightech battery charger but i dont plan to use it anytime soon. The electrical on the boat is a basket case so until i work it all out the batteries will just need to be charged by the alternator.
I will check on which alternator i have. All i can remeber about it is that it looks old. :thumbsup:

[sastanley]

Tommy, It depends on which alternator you have. The stock Motorola regulator bolted on to the alternator only charges at about 13.8v, which is "low" by today's charging standards. Not too many of those are still around though...I have an adjustable regulator on my Motorola and can set the output voltage. However, it is not a "smart regulator"..

Anyway, just sparking some discussions..with a little more details we can probably figure it out.

[Sam]

My old Morgan is on mooring can for 40+ years so I have to rely on the alternator to charge batteries. Alternator was upgraded and rebuilt to 55+ amps years ago. For the last 10 yrs have had one Optima blue top D34M and one lead acid Delco Voyager using a standard battery selector switch, 1-2 or both. Admittedly I never use the "both" setting, go out on "1" & return on "2" so each battery gets used and charged on each sail. Just recently changed out the 10 year old Delco [still held a 70% + charge] for a new Optima. You should not have a problem if batteries are kept separated.

[joe_db]

Has anyone used AGM batteries with their A4?
I have an extra new one from another boat that I was thinking of swapping into the sailboat. I am a little worried that the A4 alternator will over charge the AGM and destroy it. If I am better off leaving my flooded batteries in there I will.

Thanks for any insight.

AGMs are easier to deal with than gel batteries. They will tolerate charging voltages that will kill a gel battery. They also don't last as long as gels.
If you don't have an alternator regulator and battery charger that can be set for gel voltages, AGM is your only choice if you want to get away from wet cells. What kills AGMs is *undercharging*. Gels will tolerate that fairly well, but AGMs do not. If you are on shore power with a battery charger, shouldn't be an issue. If you use AGMs out on a mooring, you really need a solar panel to top them up.
As for mixing battery types, there are two issues. One is the charging voltages are likely different, so one of them is not optimal. The other issue is the resting voltages will be different, so the one with the higher voltage will discharge into the one with the lower voltage when paralleled and not charging.

* hint for cheap sailors* The group 31 AGM that Sam's Club has with a goofy store label (maybe Energizer?) is the exact same as a Deka marine battery that West sellls for twice the price!

[sastanley]

I have been perfectly happy with my two Gr29's wired in parallel for house (230 AmpHours), and a Gr24 start. We do not have refrigeration or any other large draws, except the occasional laptop inverter/iPad charger, etc, YMMV.

For amp/hours to the $$, I have not found a good reason to get away from flooded batteries yet. 6 volt golf cart batteries are an even better deal than 12v

AGM's are cool, but I think they require a bit more thought on the charging. I have my regulator set at 14.15v and let the ol' Motorola take care of the rest.

[roadnsky]

Tommy-
You might be well served by reading thru this technical manual from Lifeline.
It gets pretty "techy" but has some good info.
Especially related to AGM batteries.