House Bank: AGM vs. Flooded/Inverter too?

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mixman

mixman

Senior Member
Joined
May 12, 2014
Messages
122
Location
USA
Vessel Name
Pineapple
Vessel Make
Gulfstar 36 Mark II
36' Gulfstar twin diesel trawler w/ 4.4kw generator. I'm beginning a refit and trying to size a house bank. On my present 30' power cat I've got 3 group 31 flooded batteries for 315 amp hours of power. That along with 235 watts of solar and a 2k Honda generator work very well for extended periods away from the dock. With the larger boat I will most likely want to have closer to 600 amp hours in the house bank. There's 250 watts of solar so far and I will likely add more along with a wind generator I have and am considering installing. We anchor quite a bit and this boat will be used for cruising. My concerns/questions are:

1 - I tried AGM batteries on my cat and they lasted one season before losing all capacity. They were charged with a smart charger set to AGM. But as Cruising World tests have shown, AGM batteries do not do well when not fully recharged after every discharge. This is not very practical for a boat at anchor. I've heard some AGM batteries do better than others with equalizing and partial recharges. I like AGM batteries for their low-maintenance aspects as well as high charge rates, but going through a house bank every year is not going to fit the cruising budget very well. Has anyone had luck with AGM batteries in this scenario?

2 - The boat came with a 70-amp inverter/charger (pure sine wave, 2000 continuous, 4000 peak watts). The current refrigeration system is 110v. I'm used to 12v everything. How have experiences been using an inverter/charger to run some systems at all times instead of going 12v for things like entertainment and refrigeration?

Thanks!

--Kurt
 
There is nothing unique about partially recharged AGMs failing prematurely. That is a property of all lead acid batteries. But with your system I am surprised it happened. Good AGMs should last five years if treated right. Same as flooded cells.

I would charge those batteries in the morning up to about 85% state of charge (SOC) using your generator through the 70 amp inverter/charger. Then let the solar panels top them off during the day. A few cloudy days won't hurt anything if you only get them up to 85%.

The Group 31s if they are not AGMs may not be true deep cycle. Very few are. I like golf cart batteries. You know that these are true deep cycle. I add water twice a year to mine, so no big deal.

Wind chargers usually don't work well unless you are in the Caribbean trade winds.

120v appliances like a refrigerators are usually half or worse as efficient as a good 12V system. If you use your boat on the hook a lot, consider changing it out for a Frigoboat system with their keel cooler and smart speed control. The amphours should drop by a third with that system.

Use a small inverter (so you don't have the big parasitic losses of a big one) to power a TV or similar.

David
 
Thank you, David, I appreciate the input. We've had great luck using a 1000w inverter on our 30' cat so I must agree with your opinion on that issue. As for the AGM problems I had, I always did charge them back to nearly 90% each day we were at anchor. I've had no problems at all with East Penn flooded batteries that replaced them and I treat them the same way. I suppose there's a chance I got some bad batteries but Practical Sailor tests have come to the same conclusions/results.
 
mixman said:
36' Gulfstar twin diesel trawler w/ 4.4kw generator. I'm beginning a refit and trying to size a house bank. On my present 30' power cat I've got 3 group 31 flooded batteries for 315 amp hours of power. That along with 235 watts of solar and a 2k Honda generator work very well for extended periods away from the dock. With the larger boat I will most likely want to have closer to 600 amp hours in the house bank. There's 250 watts of solar so far and I will likely add more along with a wind generator I have and am considering installing. We anchor quite a bit and this boat will be used for cruising. My concerns/questions are:

1 - I tried AGM batteries on my cat and they lasted one season before losing all capacity. They were charged with a smart charger set to AGM. But as Cruising World tests have shown, AGM batteries do not do well when not fully recharged after every discharge. This is not very practical for a boat at anchor. I've heard some AGM batteries do better than others with equalizing and partial recharges. I like AGM batteries for their low-maintenance aspects as well as high charge rates, but going through a house bank every year is not going to fit the cruising budget very well. Has anyone had luck with AGM batteries in this scenario?

2 - The boat came with a 70-amp inverter/charger (pure sine wave, 2000 continuous, 4000 peak watts). The current refrigeration system is 110v. I'm used to 12v everything. How have experiences been using an inverter/charger to run some systems at all times instead of going 12v for things like entertainment and refrigeration?

Thanks!

--Kurt
Click to expand...
Based on the datasheets and Practical Sailor, carbon foam AGM batteries can be partially re-charged without diminishing capacity. This makes them ideal for cruisers where full recharge may only happen once every few dozen cycles.

Our AGMs (Northstar) are on their 8th year. They may be nearing the end of life, but I suspect I will get a couple more years out of them. We typically use 250 - 300 amps at 24vdc per day. The bank is 1250 amps, and since they have been only discharged to around 25% and then fully charged almost always they have lasted well.

I suspect the 120 vac refer is putting an enormous load on the bank you have and may explain the shortened life.
 
My negative experience with AGM batteries was with all 12v loads on my smaller boat. The refer question was related, but perhaps should have been its own topic.

I'll re-read the PS articles as I do remember some AGM batteries performing better than others. Sadly, this boat came with 4 brand new Deka made AGM batteries (designed for cell/mobile phone towers, but basically Group 31) that have yet to be installed and are fully charged sitting in storage. Deka (East Penn) was the brand that performed the worst in PS testing (and in my own experience).
 
mixman said:
My negative experience with AGM batteries was with all 12v loads on my smaller boat. The refer question was related, but perhaps should have been its own topic.

I'll re-read the PS articles as I do remember some AGM batteries performing better than others. Sadly, this boat came with 4 brand new Deka made AGM batteries (designed for cell/mobile phone towers, but basically Group 31) that have yet to be installed and are fully charged sitting in storage. Deka (East Penn) was the brand that performed the worst in PS testing (and in my own experience).
Click to expand...

Carbon foam is a fundamentally different kind of AGM that seems ideally suited to how batteries are used on a boat.
 
What percentage of the batteries capacity did you use? As already mentioned, drawing down to 75% usually guarantees a much longer life. Drawing down below 50% routinely will dramatically shorten the expected life.

Ted
 
I never took the AGM bank below 50% (monitored with a Xantrex Link Pro).
 
To my mind the key reason for AGM is their higher charge acceptance rate.

A really huge alt can cut the noisemaker time way down.

But its usually cheaper to upgrade the reefer and use the SOC meter as a guide.

Now that you are in a monohull weight is not a danger so a couple of pounds of batts is no big deal.
 
mixman said:
1 - I tried AGM batteries on my cat and they lasted one season before losing all capacity. They were charged with a smart charger set to AGM. But as Cruising World tests have shown, AGM batteries do not do well when not fully recharged after every discharge. This is not very practical for a boat at anchor. I've heard some AGM batteries do better than others with equalizing and partial recharges. I like AGM batteries for their low-maintenance aspects as well as high charge rates, but going through a house bank every year is not going to fit the cruising budget very well. Has anyone had luck with AGM batteries in this scenario?
Click to expand...


Our oldest bank of 3x Odyssey G31 AGMs (PC-2150s) is just now ending it's 10th season. This is a multi-purpose bank: starboard engine starting, half the house loads including one fridge, and bridge electronics load. Seems healthy.

That said, we don't anchor out as often as we'd like. When we do, it's easy enough to run the genset 2x/day to recharge anyway (while making breakfast and dinner). And then we're back at the dock and on shore power usually after 3 days or so.

That said, we don't have solar.

Our charger is original to the boat, only a 40-amp jobbie, not up to recommended standards for our total amp-hour capacity, but it seems to be doing the job. There's no separate setting for AGMs; manual says to use the flooded lead-acid setting for AGMs and that' what we've done.

I've begun planning for replacement when necessary; probably 4x 6V Lifeline GC-2 golf cart equivalents. Partly because increasing "house" capacity on that bank from 300 to 440 Ah would be a good thing (and I can add an inverter/charger, to address that charging capacity issue). Partly because I can probably fit those into the same general area, whereas I couldn't add another G31 there. Partly because that combination still gives me enough cranking amps to meet minimum engine starting requirements. Partly because Lifelines can be equalized.

-Chris
 
AGM batteries do not do well when not fully recharged after every discharge.

ALL batts need to be brought to 100% as often as you can LA included.

For most cruisers this is not possible so the 85% full becomes the goal, which limits the juice you can use daily.

85 down to 50 is lots less than 100 down to 50.

The EZ solution is a bigger batt bank so 85 down to 50 is comfortable with your daily house requirements.

4 or 8 6v golf cart batts usually will do for folks with a sail cruising background.
 
In my experience the advantages of AGM batteries over flooded batteries have never been worth the large price premium for AGMs. I am still using flooded batteries and generally get 8-10 years from a set. My solar panels tend to keep my batteries near 100% charge except when I am running the boat for multiple day trips. My battery banks are sized so that I don't go below 75-80%. Keeping your charge state up really helps with battery life.
 
The first question in sizing a bank is your daily budget of amp hours to be used.

The second is your daily budget of amp hours put back.
 
I replaced my four 4D AGMs with four Crown CR-235s. I use about 65ah a day, this gives us about 3 days between needing a charge. I only have a 8kw generator with a 100 amp charger, no solar or wind.
 
Excellent input, thanks! I'm toying with a 200-ish amp hour bank for reserve & starting (genset will have its own battery for emergency purposes) and a primary 400-600ah bank as the main house bank. With a 70-amp charger, solar (planning on 400 watts) and wind generator, I'm not going to be blasting amps into the main house bank to take advantage of AGM batteries. I'm thinking I'll stick with lead-acid to start. Granted, I've got 4 fully charge, 1 year old AGM batteries in storage that I somehow need to take advantage of. They're an odd configuration with odd terminals as they're built to be backup power for cell towers (they're East Penn/Deka brand). I could install them but once they fail I'd have to reconfigure everything terminal and mounting-wise. Perhaps it is time for eBay for those? :)
 
mixman said:
Excellent input, thanks! I'm toying with a 200-ish amp hour bank for reserve & starting (genset will have its own battery for emergency purposes) and a primary 400-600ah bank as the main house bank. With a 70-amp charger, solar (planning on 400 watts) and wind generator, I'm not going to be blasting amps into the main house bank to take advantage of AGM batteries. I'm thinking I'll stick with lead-acid to start. Granted, I've got 4 fully charge, 1 year old AGM batteries in storage that I somehow need to take advantage of. They're an odd configuration with odd terminals as they're built to be backup power for cell towers (they're East Penn/Deka brand). I could install them but once they fail I'd have to reconfigure everything terminal and mounting-wise. Perhaps it is time for eBay for those? :)
Click to expand...

Do they have "flag" terminals? In other words turned up 90 degrees with a hole in them or a round crimp on terminal..
 
Last edited:
We installed 4-8D Deka AGM's in our Californian in 2008. Our battery banks are located on the outboard side of our engines; hard to service wet batteries in that position. AGM's solved that issue. We spend 90% of our cruising time at anchor; So far, we have had great results. We don't have AC, or a genset, but do run a Norcold 12v refrigerator while anchored.
 
Moonstruck said:
Do they have "flag" terminals? In other words turned up 90 degrees with a hole in them or a round crimp on terminal..
Click to expand...

Nah, they're tiny terminals. I have lugs that fit them from the seller I got them from with the boat, but they're a far cry from "marine grade" connections.
 
chc said:
We installed 4-8D Deka AGM's in our Californian in 2008. Our battery banks are located on the outboard side of our engines; hard to service wet batteries in that position. AGM's solved that issue. We spend 90% of our cruising time at anchor; So far, we have had great results. We don't have AC, or a genset, but do run a Norcold 12v refrigerator while anchored.
Click to expand...

I seriously wonder why I had such problems with 3 Deka (East Penn) Group 31 AGM batteries then. I replaced them (under warranty) with 3 LA Deka 31s over 2 years ago and have had no issue since. You make me want to try the 4 Dekas I have in storage. I guess I don't have much to lose.
 
You make me want to try the 4 Dekas I have in storage. I guess I don't have much to lose.

Have they been kept charged?
 
They have been off charge for a few months but have a resting voltage of 12.8 to 12.9 volts. If I don't install them in the next few weeks I will put a trickle charger on them.
 
A battery observation that I made yesterday. I own/operate heavy equipment and noted a weak 12v battery yesterday in a D3 Caterpillar Bulldozier. Exposed the battery and found it to be original caterpillar battery 16 years old. Recharged it and waiting to see if I can get a few more years out of it.
 
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