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Old 21-07-2017, 13:22   #1
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Gel vs AGM batteries for house bank

Hi, I have 4 Exide Gel batteries, 120Ah each as a house bank, they came with the boat when I bought her last year. Now 4 years old.
My solar panels charge them to a 13.5/7 V during the day, but by around 7 or 8 pm I see the charge go down to 12.9 V - about an hour after sunset. They keep dropping charge and at 11 pm I'm down to 12.6/12.5 V So here's when I run the genset for about an hour, because I don't like to go under 12.5V and if I don't run it, by 8 am I'm at 12.3 V or even less ...
My lights are all LED, I have two refrigerators running non stop (about 8Ah combined) Waterpump and heads are electric so with a family of four living on board at anchor, the evenings do put a dent in the battery bank after 4 bathroom visits, but still ...
Question 1 : Can I safely say my gel batteries are toast if they can't hold a charge like this, however only 4 years old ?
Question 2 : And if I should replace the house batteries; people say gel is perfect for house banks, AGM is more versatile but better for starter batteries. However, Budget Marine Here in Curacao says they haven't sold gel batteries in the last 3 years or so !?
Any advice is much appreciated. Thanks !
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Old 21-07-2017, 13:32   #2
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Re: Gel vs AGM batteries for house bank

Actually they sound in good shape; a fully charged gel cell will be about 12.65 or so; at 12.3 they are still over 50% charged... and, I'm guessing, these are with a load so the resting voltage is actually higher. Read the battery section of Nigel Calder's manual (4th edition has an extended battery sections).
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Old 21-07-2017, 14:11   #3
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Re: Gel vs AGM batteries for house bank

The limited information in your post says that the batteries are working pretty much as they should. I bet there are some phone, computer and camera chargers running during that time as well. There is nothing wrong with showing 12.3 volts at 8 am.

Three tips for the future :
1. AGM works best on boats at a dock because they like regular 100% charge. If you are mostly anchored or moored then stick with gel.
2. Whenever the house bank is replaced add two more batteries to raise the AH. What you have now isn't big enough for the heavy use that your family is giving the system.
3. Think about trashing the electric head. Those things really chew through both electricity and fresh water. I understand that the threats from the Admiral might make this difficult. With a manual head you won't need extra batteries.
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Old 21-07-2017, 14:54   #4
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Re: Gel vs AGM batteries for house bank

i have same 4 batteries.

Have 1 fridge and manual toilets and no generator.

360W solar gets it to float 80+% of days before sunset.
In the morning after using 50Ah overnite and no load, voltage is 12.5V.

If your have load when you check voltage, this decreases voltage. When my fridge turns on at night, voltage drops 0.1V. So in the morning with fridge running get 12.4V.

Check for battery docs on internet for expected voltages. This batteries meant to last 6-9 years if you keep drawdown below 75 AH overnight with few exceptions.

It looks to me your batteries are still ok. Mine see no sign of weakness after 4.5 years but used lighter.
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Old 21-07-2017, 15:02   #5
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Re: Gel vs AGM batteries for house bank

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Originally Posted by Scott Berg View Post
Actually they sound in good shape; a fully charged gel cell will be about 12.65 or so; at 12.3 they are still over 50% charged... and, I'm guessing, these are with a load so the resting voltage is actually higher. Read the battery section of Nigel Calder's manual (4th edition has an extended battery sections).


Yes Scott, there's always a load on through the refrigerators, we live on board throughout the year. But discharging them daily to or below the 12.3V line, is that OK ? Thanks for the Calder lead, I'll have a look.
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Old 21-07-2017, 15:40   #6
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Re: Gel vs AGM batteries for house bank

You can discharge to 12.2 resting
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Old 21-07-2017, 15:53   #7
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Re: Gel vs AGM batteries for house bank

Get a SmartGauge or a shunt-based SoC monitor to really know how you're caring for whatever bank you happen to be using at the time.
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Old 21-07-2017, 16:49   #8
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Re: Gel vs AGM batteries for house bank

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Originally Posted by savoir View Post
The limited information in your post says that the batteries are working pretty much as they should. I bet there are some phone, computer and camera chargers running during that time as well. There is nothing wrong with showing 12.3 volts at 8 am.

Three tips for the future :
1. AGM works best on boats at a dock because they like regular 100% charge. If you are mostly anchored or moored then stick with gel.
2. Whenever the house bank is replaced add two more batteries to raise the AH. What you have now isn't big enough for the heavy use that your family is giving the system.
3. Think about trashing the electric head. Those things really chew through both electricity and fresh water. I understand that the threats from the Admiral might make this difficult. With a manual head you won't need extra batteries.


Yep, the inverter is on as well and indeed the gadgets get recharge over night ...
So a bit of good news then, my wallet was in a cold sweat already.
We're anchored or on a ball most of the time, so I'll stick to gel.
Adding two new batteries now to an old bank is probably not the way to do it, right ?
I did think about losing the two (!) electric heads - they use seawater though - but the force of the Admiral is strong in this one ...
Thank you for the advice !
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Old 21-07-2017, 16:49   #9
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Re: Gel vs AGM batteries for house bank

savoir makes a good point about AGMs liking to be regularly back to 100%. Also they really prefer to be charged fast when in bulk. 0.2C (96amps for your system) would be the minimum you want to charge at. That's about 1200w of solar.

https://forums.sailboatowners.com/in...choice.124973/
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Old 21-07-2017, 16:56   #10
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Re: Gel vs AGM batteries for house bank

Voltage is a lousy indicator of state of charge. You NEED a amp hour meter, or smartguage to know what state your batteries are in. GELS are really quite tough, but without accurately knowing the soc, you are gambling with you batteries.

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Old 21-07-2017, 17:05   #11
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Re: Gel vs AGM batteries for house bank

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Adding two new batteries now to an old bank is probably not the way to do it, right ?
Throwing money down the electric toilet.

Invest in the Soc monitor, start logging and saving aggressively for a replacement bank.

See what you can do to stay above 50%, or it may need expanding.

More charge source may be required, instead or as well, the BM will lead to an informed decision rather than WAGing
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Old 21-07-2017, 17:18   #12
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Re: Gel vs AGM batteries for house bank

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You can discharge to 12.2 resting
Correct.

Except for under cyclic load.

You don't have a problem.

Read Maine Sail's website: https://marinehowto.com/

Interestingly enough, the top subject is right up your alley.
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Old 21-07-2017, 18:11   #13
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Re: Gel vs AGM batteries for house bank

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Originally Posted by Stu Jackson View Post
Correct.

Except for under cyclic load.

You don't have a problem.

Read Maine Sail's website: https://marinehowto.com/

Interestingly enough, the top subject is right up your alley.


Wow. Very clear and detailed article, thanks. My mind is now spinning a little bit though
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Old 21-07-2017, 18:26   #14
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Re: Gel vs AGM batteries for house bank

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Originally Posted by john61ct View Post
Throwing money down the electric toilet.

Invest in the Soc monitor, start logging and saving aggressively for a replacement bank.

See what you can do to stay above 50%, or it may need expanding.

More charge source may be required, instead or as well, the BM will lead to an informed decision rather than WAGing


My system is Mastervolt, with a shunt based SOC monitor through their MasterBus link. After the advice I read here I conclude I need a bigger house bank; 200 to 300 Ah more than what I have now, ánd some extra solar to top things of... But as you point out my housebank is still OK for now, I still have time before I have to break that other, already oh so suffering bank ...
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Old 21-07-2017, 19:49   #15
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Re: Gel vs AGM batteries for house bank

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Originally Posted by jugga View Post
My system is Mastervolt, with a shunt based SOC monitor through their MasterBus link. After the advice I read here I conclude I need a bigger house bank; 200 to 300 Ah more than what I have now, ánd some extra solar to top things of... But as you point out my housebank is still OK for now, I still have time before I have to break that other, already oh so suffering bank ...
So what are the SOC percents for the times and voltage values that you posted in your original post? Are you seeing something like 100% to 50-60%?
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