New AGM batteries - what am I doing wrong?

[Derek Lumb]

While any of the suggestions may be part of the problem, another thing to consider is that Lead Acid batteries have a self discharge rate; in other words, left on the shelf they will slowly discharge. The rate of this is related to temperature and so while at modest temperatures(25deg C) the shelf life is typically around a year, this falls to about 5 months at 40 deg C and ~2 months at 50 deg C. So if your batteries were stored in hot conditions, without recharging, before you bought them, they could already be degraded severely.

[scottburch]

This may be a bad suggestion given your batteries are new, but if you can, I would swap them out for LiFePo batteries. I did that last year and would never go back to AGM again. We are full time at anchor in Mexico, and they changed our life. We replaced them with Battle Born batteries.

* You don't need to charge the to 100% to keep them healthy
* You get at least double the amp hours for the same rating
* They are rated about about 10 times the cycle life
* They accept the full amps from our solar longer (so we get a lot more power stored)

We went from running the generator every day to every three days.

We went from ~600 amp hour AGM to ~800 amp hour LiFePo4 and have about 3 times the power in the same space.

The reason for the extra power is that you can discharge them further and they hold a higher voltage. Our LiFePo is rarely below 13.1v and they hold a higher voltage under a heavy load. They drop about .3 to .4 volts under a 200 amp load.

If you are already set for AGM charging (maximum of 14.4v) then you are already set for the Battle Born batteries.


The only down-side so far was the price, they are about 3 times more expensive, but we figure we will make up for that in less fuel and longevity.

[Wildcats]

As others have pointed out we don't have enough information to know the cause of your premature and inadequately charged batteries. It is clear that if you have shore power and when you leave the dock your battery state of charge is only 12.5 volts you have a charger problem. Pro Mariner inverter/chargers in my experience ( I had one) are poorly made. Mine rusted out in two years (it has a steel case) and the bithermal circuit breaker constantly kicked out at half of the unit's rated wattage capability.



For an AGM battery that is new the open circuit voltage should be 13.0 volts, i.e. this is a battery not connected to a charger and has no loads on it and has rested for 4 hours.



Charging to less than the 100% rating of your AGM battery will eventually lead to sulfation and premature death of your batteries. AGMs are expensive.


Suggestions:
1) Pony up for a good charger or charger/inverter such as the Magnum. In the long run you will make up the additional expense in buying fewer batteries.
2) AGM batteries should be brought up to a full state of charge, doing less than that leads to early death of the battery. This should be about 13 volts.

3) Buy an excellent AGM house battery like the Concorde Lifeline battery. They make a group 31 battery, the GPL 31XT that is rated at 125 amp hours (20 hour discharge rate). For a battery bank such as yours, you would have 375 amp hours and you could safely use up to 187 amp hours before reaching a 50% state of charge which is 12.2 volts.
4) I would encourage you to download the technical manual from Concorde Lifeline regarding AGM batteries, it is the best manual I have ever read for the care of AGM batteries (specifically theirs but good general advice). The link for this manual is: https://321166-984045-raikfcquaxqnco...al-5-06-19.pdf

[DeValency]

Originally Posted by aisleorwindow

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?

The loss of battery power over 4-5 hours with all the consumers described is reasonable. Remember the usable power out of the 300A batteries is at the most ~1.4-1.6Kw until dropped completely to levels that risks the batteries health. So on a trip like that with all the consumption you may want to start the engine every 2-3 hours to recharge for ~30 min and it should normally go over 13-13.5V. - for healthy batteries.

Three group 31 AGM house batteries should be enough for day/coastal sailing but you need to make sure they are charged well at all times to over 12V.

And when the time comes, replace to LFP batteries - you'll never want to return to flood batteries again.

[aisleorwindow]

Thanks again for all the contributions to this thread, here's an update, admittedly some of this is a bit embarrassing, but hopefully other newbies can learn from my errors:

What I originally thought was a bank of 2 engine batteries on the Starboard side of the boat and a bank of 3 house batteries on the Port side of the boat, were actually 1 engine battery + 2 house batteries on the Port side.

The 2 batteries on the Starboard side of the boat are optional/extra house batteries. see below (nevermind that port and starboard are switched in the manual )

https://photos.google.com/share/AF1Q...VFbGVZaWhhTkxR

So I disconnected everything to check each battery individually. These "optional" batteries were the old batteries and are reading at 12.55 volts.
The new batteries are all showing 12.9 - 13+.

So I figured if I disconnected the old ones, and just used the two new house batteries, which I know are 12.9+, that might solve the problem - i.e. the old ones were "dragging the new ones down."

So after doing that, my new house batteries were reading at 12.77 or so, but my battery monitor was showing that I was only at 12.4, using 3-4Amps.
Then I turned on my MFD/instruments and that added another 4 amps or so. My batteries immediately started dropping to 12.6, then 12.5 using my batter tester.... my monitor showed 12.2.

So at this point I'm not sure what exactly is going on:

Have I already ruined my new batteries?
Is something drawing on them higher than it should be?
Is my battery monitor incorrect? (not sure why the monitor number doesn't match my battery tester reading)

A few other data points:
The the engine battery and auxiliary battery (for windlass/bow thruster) are totally fine. So that leads me to believe it is not an issue with the charger and/or alternator.
The "old" batteries are the exact same type/brand as the new ones (Deka AGM 31s - 100AH). Embarrassingly I may have killed them as I left them on the boat all winter in Chicago - so that may be why they are only at 12.5?

Anyways, going to charge everything overnight and come back tomorrow and see how things look.

Go easy on me, I know some of you old salts must be shaking your head at me, but hopefully someone else can learn from this. I'm a pretty smart guy in many areas, but I know I'm not alone in being utterly baffled by electrical systems.

Again, thanks to all for their help (and patience!) with my journey.

[Adelie]

Figure 50Ahr/day average draw each for fridge and autopilot.

[Adelie]

Also, AGMs are not a good choice for sailboat service unless you motor a lot.
They don’t like:
A. PSoC service (Partial State of Charge), ie not being fully recharged almost every cycle. Firefly/Carbon Foam AGMs are resistant to this but cost a lot more.
B. Low-C bulk charging. They should be recharged at 0.2C minimum (20Amps for every 100Ahr capacity, so 60Amps for a 300Ahr bank), 0.3-0.4C would be better. That means you need a high output alternator and probably a serpentine belt to drive it and a smart regulator. Even Firefly’s need high-C charging or cycle life will suffer.

For those that don’t know bulk charging is when the battery bank will accept as much amperage as the alternator can put out. Generally this is from about 50% state of charge up to around 75%. For FLAs and Gels this should be 0.13C or less. Voltage will be below the target voltage of about 14v but will slowly rise until it gets to target at which point bulk charging ends and the regulator limits voltage to avoid damaging the battery. This is call absorption charging and amperage slowly tapers off.

[ranger58sb]

Originally Posted by aisleorwindow

The "old" batteries are the exact same type/brand as the new ones (Deka AGM 31s - 100AH). Embarrassingly I may have killed them as I left them on the boat all winter in Chicago - so that may be why they are only at 12.5?

AGMs don't self-discharge all that much, so over winter on the hard with no charging could be no big deal.

Maybe they're only at 12.5 because your charging source isn't (sufficiently?) charging them?

-Chris

[aisleorwindow]

Well I'm still stumped on all of this. Battery charger is on correct settings. It's a Cristec CPS3OEM 12v 60A charger that is the original that came with the boat (~10 years old). I've tried turning the "Boost" function off to see if maybe the batteries need to be charged more slowly, but that didn't make any difference.

Going to have to call in an electrician, do a load test and try and figure it out.
I'm wondering if the battery charger may need to be replaced.

[ranger58sb]

Originally Posted by aisleorwindow

Well I'm still stumped on all of this. Battery charger is on correct settings. It's a Cristec CPS3OEM 12v 60A charger that is the original that came with the boat (~10 years old). I've tried turning the "Boost" function off to see if maybe the batteries need to be charged more slowly, but that didn't make any difference.

Going to have to call in an electrician, do a load test and try and figure it out.
I'm wondering if the battery charger may need to be replaced.

Originally Posted by ranger58sb

Do you know for sure your shorepower charger is working?

Do you know for sure your engine alternator is working?

-Chris

I can't tell from reading back through the thread...

Without regard to battery charger settings...

Did you put a multi-meter on the battery terminals -- with no load, and with the battery charger connected and turned on?

If so, did it show voltage in the area of 14.7-ish or so? (Bulk/absorption approximate)

Or maybe 13.5-ish or so? (Float approximate)

-Chris

[aisleorwindow]

Originally Posted by ranger58sb

I can't tell from reading back through the thread...

Without regard to battery charger settings...

Did you put a multi-meter on the battery terminals -- with no load, and with the battery charger connected and turned on?

If so, did it show voltage in the area of 14.7-ish or so? (Bulk/absorption approximate)

Or maybe 13.5-ish or so? (Float approximate)

-Chris

Sorry, just reread your post. I did not do that. I can certainly do that. For my education, what would that tell me?

[ranger58sb]

Originally Posted by aisleorwindow

Yes I did and the answer is the latter (float approx) - although it was less than 13.5 - closer to 13.

Originally Posted by aisleorwindow

Sorry, just reread your post. I did not do that. I can certainly do that. For my education, what would that tell me?

If you haven't done this...

Try discharging your batteries a bit... intentionally get them down to 12.4 or 12.5... then turn on the charger and check then. Intent is to force your charger to go into bulk rate.

If voltage doesn't rise to your bulk/absorption setting (modified a bit by temp compensation), then your charger probably isn't.

I'd guess 13.0-ish at float isn't great either, although it does somewhat depend on what your settings are (Lifelines, for instance, don't want a high float) and there's that temperature compensation thing...

-Chris

[MJH]

Originally Posted by aisleorwindow

Well I'm still stumped on all of this. Battery charger is on correct settings. It's a Cristec CPS3OEM 12v 60A charger that is the original that came with the boat (~10 years old). I've tried turning the "Boost" function off to see if maybe the batteries need to be charged more slowly, but that didn't make any difference.

Going to have to call in an electrician, do a load test and try and figure it out.
I'm wondering if the battery charger may need to be replaced.

You need to understand how your electrical system is working to really answer all your questions. The SIMPLEST system is two banks, one for start and one for house. Each bank can be made up of any number of individual batteries. The house bank should be bigger and power everything else, the start bank is just for starting. So, I recommend removing your old batteries from the boat for now.

You stated that the battery charger settings are OK...I presume the switches are setup for AGM. So that tells me when you depart the dock your batteries should be fully charged; what are those voltages? As soon as you start turning on electronics or whatever you are using Amp hours and the voltage will start dropping unless there is comparable electrical input like from your engine alternator. How big is it? Its all a matter of what goes out being match by what comes in.

You have not mentioned if you have a SMART REGULATOR and if you have checked the settings.

Hang in there.

[MikeHoncho]

Originally Posted by goboatingnow

The curse of the undercharged AGM strikes again. Agms get damaged if not recharged regularly to 100%. As I have opined , they are not a good fit for boats.

Disagree with being appropriate on a boat. I just spent two weeks with no shore power and got mine up to 100% charged per my Balmar monitor everyday with alternator and solar. Not one did I run my engine to charge the batteries. The system needs to be properly engineered. Mine is a Lifeline 8D 250 amp/hr (20hr) agm with 100 amp alt and 250 watt panels.

[Icarus]

Originally Posted by goboatingnow

The curse of the undercharged AGM strikes again. Agms get damaged if not recharged regularly to 100%. As I have opined , they are not a good fit for boats.

Correct