New AGM batteries - what am I doing wrong?

[MJH]

Originally Posted by aisleorwindow

Sorry if these questions are elementary to some, but I am trying to learn!

Bought my boat last year and it had 3 AGM 31s for house batteries, from 2015 that by the end of the season they were starting to die quickly, so replaced all 3 on May 1st of this year. Seemed reasonable to replace them as they were ~7 years old.

Wired them the same way and everything seemed to be holding well. Start at 12.5v and never going below 12.2v or so. I am mostly a day sailor so batteries are usually only relied upon for maybe up to 6 hours at a time - not overnight or anything. I always leave the boat plugged into shore power and charging.

Last weekend (so only 2.5 months since replacement) I did a longer passage (~60nm) of which we sailed the last half or so - maybe 4-5 hours. By the end of the trip I noted the batteries were down to 12.0v and even dipped to 11.9v for a few seconds.

Seems awfully quick to reach that low. We were using what I would consider "normal" load: fridge, freezer, VHF, MFD/instruments, Autopilot and a couple of fans.

Used the boat yesterday and as soon as I turned the engine off the house batteries were showing down 12.2v already.

So what am I doing wrong? Are these 3 batteries just not enough for this usage?

There is more to proper battery management than just having AGM batteries. As someone already mentioned, you probably have two house batteries and one starter battery. Two AGM 31s will give you about 210Ah for the house but that isn't really enough to run refrigeration effectively, particularly when sailing. A rule of thumb is that your alternator should be 25% of your total Ah or (3x105)x.25 = 78.75Ah rating. What size is yours? But note that the maximum Ah rating is only achieved at the higher RPMs.

You need to get a better handle on what you are using and what you are generating but for just local sailing without refrigeration the problem is elsewhere. I would get out the battery charger manual and see that it is properly set up for AGM batteries. Also look at the new battery manual/instructions to see what settings your smart regulator are and check them...you do have a smart regulator, don't you? If you don't, get one. An AGM setup is generally 14.7V for Bulk and Acceptance Phases and 13.8V for Float Phase but manufacturers differ.

Lastly, seven years is not very long for AGM batteries and speaks to their poor management. I am using 2x8D GEL house batteries and replaced them in 2019 after 15 years. But I have a Balmar smart regulator set to battery manufacturer's settings, 110A alternator with serpentine belt, smart battery charger set to GEL, LinkPro battery monitor, Automatic Charging Relay to keep the start battery charged, Alternator and Battery Temperature Sensors, and 560W of solar panels. Oh, and I don't have refrigeration.

You should be balancing the complete electrical system not just thinking of AGM batteries, their only one part.

Good Luck.

[moseriw]

Of course you can always buy proper deep cycle flooded batteries - Trojan is probably the best one.



Oh my - stay off Trojans. Every cell needs 1/8 l of water every 2 Months!
And chargers? Victron? My shunt says 97% and the batteries drop over night to 12.2V
The SmartSolar can not be adjusted to float - even if I set 12,8V as float (should be 13,6V for the Trojans.)

Looks like the Trojans are done after two years due to lack of water as the plates were blank 2x during the wintertime.

Solutions: still waiting for an input of Trojan and Victron since 3 months. The Trojan seller says plank plates should not harm the batteries - they are build for this lack of service.

So what? I am just a user an do not want to go in for a battery charge system engineer.

[Bowdrie]

Were the new batts ever "formed", that is, drawing them down and then subjecting them to a rigorous charging cycle?
That process "imprints" the + and - plates, it gives them a "memory", if you will.
How about the engine alternator?
Does it have a 3-stage regulator?
The common internal regulators are woefully slow to recharge a batt, they're mostly designed to just replace what the starter used and then carry any loads.
That's why you can drive your car cross country never shutting the engine off, and you don't boil the cells, the voltmeter can show 14 volts but the currant is at a microscopic level.

[StuM]

> Start at 12.5v

There's a problem for a start. The AGMs are never getting above about 70% SOC.
They will have degraded very quickly.

[goboatingnow]

AGMs are not a good fit for boats and certainly around me wet VRLA is by far the most common fit. Good quality AGMs will last li gwr but are still damaged by partial charge cycles.

AGMs were not designed for boat style operations , why they were pushed into this market is beyond me.

Just buy decent ( Bosch, Varta) sealed wet batteries. Or do like me an buy cheap ones and bin then every 4-5 years. Last year I bought two 140 AH for €200 total , Cash.

[FionaJC]

I wonder if your charging the AGM's at the right voltage. I charge them through a DC to DC charger off a shore charger or alternator. My solar is through a MPT set for AGM. Check current draw and charging voltages for your batteries. Check voltages individually after a full charge - disconnect them first to check voltages.

[goboatingnow]

Originally Posted by FionaJC

I wonder if your charging the AGM's at the right voltage. I charge them through a DC to DC charger off a shore charger or alternator. My solar is through a MPT set for AGM. Check current draw and charging voltages for your batteries. Check voltages individually after a full charge - disconnect them first to check voltages.

The issue isn’t the voltage per se. The charging system must have the time and capacity to fully recharge AGMs on a regular basis. Unlike other forms of LA tech , AGMS are disproportionately damaged by undercharging , a situation that’s very common on boats.

[FionaJC]

Originally Posted by goboatingnow

The issue isn’t the voltage per se. The charging system must have the time and capacity to fully recharge AGMs on a regular basis. Unlike other forms of LA tech , AGMS are disproportionately damaged by undercharging , a situation that’s very common on boats.

I replaced my lead acid batteries with AGM's. I only got two seasons out of LA but Im on three with the AGM's using the above system. I only get to shore charge once a year and alternator when out. I had two years of only solar charging when installed and they have been fine.

[goboatingnow]

Originally Posted by FionaJC

I replaced my lead acid batteries with AGM's. I only got two seasons out of LA but Im on three with the AGM's using the above system. I only get to shore charge once a year and alternator when out. I had two years of only solar charging when installed and they have been fine.

Firstly two seasons out of LA is extraordinary poor and suggests something is wrong with your setup. Hence 3 years on AGM doesn’t actually point to anything one way or the other . How do you know they are “ fine “. Degradation can be hard to determine until it’s close to the end. AGMs technically when used within their specs should give upwards of 8-10 years.

[CarinaPDX]

Originally Posted by goboatingnow

Firstly two seasons out of LA is extraordinary poor and suggests something is wrong with your setup. Hence 3 years on AGM doesn’t actually point to anything one way or the other . How do you know they are “ fine “. Degradation can be hard to determine until it’s close to the end. AGMs technically when used within their specs should give upwards of 8-10 years.

Living in the UK I think Sonnenschein Prevailer gels are the way to go for Fionna. They are far less sensitive to the charging regime than AGMs but otherwise have the same advantages over flooded.

BTW I think AGMs got started in the marine world with military use. AGM batteries are very resistant to vibration damage and are a good match to small(-ish) high speed boats that can pound the life out of other batteries. That is not a problem on cruising sailboats.

Greg

[goboatingnow]

Originally Posted by CarinaPDX

Living in the UK I think Sonnenschein Prevailer gels are the way to go for Fionna. They are far less sensitive to the charging regime than AGMs but otherwise have the same advantages over flooded.

BTW I think AGMs got started in the marine world with military use. AGM batteries are very resistant to vibration damage and are a good match to small(-ish) high speed boats that can pound the life out of other batteries. That is not a problem on cruising sailboats.

Greg

I’m not a fan of gel batteries. Yes they do not have the issues with undercharging that AGMs have. But they are very sensitive to overcharging

I fail to see what’s wrong with good old wet acid VRLAs.

[CarinaPDX]

Originally Posted by goboatingnow

I’m not a fan of gel batteries. Yes they do not have the issues with undercharging that AGMs have. But they are very sensitive to overcharging

I fail to see what’s wrong with good old wet acid VRLAs.

Being sensitive to overcharging is simply not an issue with proper charge regulation. I can charge my batteries with a battery charger, alternator, wind, and solar; each has its own regulation which is set to limit charge voltages to 14.2V (the manufacturer's recommendation). The advantage to gel is that little thing called internal resistance. I suspect most people like gels for the fast charge rates but for me it is in discharge use that these batteries shine. I only have three batteries aboard, group 29/31/30H depending on availability, and I typically operate the house with just two of them. With my old Rolls 30H (130Ah each IIRC) batteries my ham radio (100W) would sometimes sag the voltage and cause distortion. With the 29 (85Ah each) gels, with substantially less capacity, the voltage stayed high regardless of the load, including the 150W SSB. While it is less of an issue today, 30 years ago there were several "12V" devices that didn't work so well when the batteries were at 50% SOC. The gels just made everything work better.

At least in theory I don't see a problem with VRLAs either. For me the main reason for not considering them is the higher internal resistance, similar to ordinary flooded. If I had a larger battery bank then that would probably not be a concern. The attraction of higher charge/discharge rates with gels and AGMs is mitigated by larger capacities of flooded cells relative to load and alternator size.

Greg

[aisleorwindow]

Thanks everyone for the helpful replies. Just to clarify, I have a Bank of three batteries for the domestic/house. And a separate bank of two for the engine. In addition, I have a separate battery bank for the windlass and now thruster. It's only the house batteries where I'm having an issue. Which leads me to believe it's not an alternator problem, nor should the battery charger be on the wrong setting (but I'll double check). So the most likely is that it's something with the new batteries. Regretfully they are not one of the premium brandd some of you recommended. It was hard to find batteries at all to be honest with the supply chain issues. I paid almost $1,000 for the three.

But anyways I'll test them out one by one and see if maybe one of them is bad. That seems like the most logical place to start. Again, thanks for the suggestions for a newbie to boat electrical. I'll report back.

[Mike Crothers]

What a lot of the replies are not saying is that we all feel your pain and most of us have learned the hard way and are still learning. Don't get discouraged or overwhelmed.



While the batteries quality may have been the issue, in the future to know for sure create a good battery log with key data. This will also help with any warranty claim.



Voltage before and after charging along with the battery temperature, how long they were charging and what the starting and ending amp flow was.



If you don't have it now, consider setting up temperature compensation on your alternator/regulator and 110V charger. The recommended voltages change with temperature.



A battery monitoring system is not expensive but it is work to install. It will help give you the above data to assist trouble shooting.



I doubt you will find one thing that solves the problem but that batteries are an ongoing challenge.

[duffy35]

Many good suggestions; I would add a battery monitor. This is similar to a fuel gage. It will show you exactly how much you have left in your battery. It will also show you how many amps are going into your battery and how many amps are coming. I have gone thru all of my electronic loads and used the battery monitor to see. For example I took a look at the battery draw of the refrigerator; it pulls 3 amps. I took all of that data and put it in a spreadsheet. I know my batteries will allow 125amp hours in total (50%) draw down as they are AGMs. If I have everything turned on I draw 55amp/hours/day. I will soon install a solar panels to replenish that 55amp/hours. Xantrex and Victron both make battery monitors. The installation of the battery monitors took all the guess work out of the State of Charge of my batteries.