I can't figure what's going on

[Ostinato]

My house bank voltage is falling very low on typical day even though the amps hour usage is within reasonable limits. By very low I mean 12.1v or less.

I have a house bank totaling 625 amp house. The banks consists of five 12v 125amp Odyssey (acid starved) GSM batteries. I don't typically let the bank fall below 450 amp hours. I use a Blue Seas VSM meter to monitor the bank's charge status. I have isolated each battery to see if one is dead - all seem fine.

I can easily charge the bank to 90% capacity at anchor based one the VSM meter and typically do.

I've read multiple times that voltage is not very meaningful in a day to day context but I feel uneasy about what I am observing. Any thoughts?

[Sandero]

Your batteries are at the end of their service life... their capacity is gone. They will accept charge appear topped off but go down pretty quickly.

Think of your battery like a glass of water and the amps as the water. Over time your glass gets full of sand which reduces the amount of water that the glass can hold. It doesn't take long to fill the sand filled glass with water... capacity has gone... and probably not recoverable anymore. You can't really dump the sand from the glass.

[Wotname]

^^
+1 to what Sandero said.

For confirmation, do a discharge or capacity test. I would be very surprised if your capacity is anywhere near the 650 AH you think you have.

[Ostinato]

That's unfortunate. The oldest of these batteries is 2011 and very expensive. In the past I've gotten 7 years out of gels. I'll think twice or three times before I replace them with the same thing.

Good to know though. Thanks.

[skipmac]

I don't think there is enough information yet to confirm you have dead batteries. First a few more details would help to determine this and a few comments might help you understand what's going on and maybe help extend your battery life.

First, how long since you have synched the battery monitor? The % state of charge on these can be very inaccurate if you have not done this recently. The best, most accurate way to synch the monitor is to fully charge the batteries and manually synch, which leads to a second question.

How long since you have fully charged the batteries AND how long since you have equalized? You are in a classic, off the grid cruisers situation which typically cycles the batteries from 50-80% or something similar. Day to day this is the most efficient way to use and charge batteries but to keep them healthy you should try to fully charge them every couple of weeks or so and equalize them every couple of months or so.

Are you also aware that the amps showing on the meter may be going to the battery but not all of that converts into charge in the battery. There are inherent losses in the conversion of amps in to the chemical recharge so if you read on a monitor 100 amps out and 100 amps back in every day, you might only be getting 90 amps of recharge on the battery leaving 10% short every day.

Voltage can be a good indicator of state of charge used correctly but in most real world situations it isn't practical because to be accurate it must be measured with no load or charge on the batteries and the batteries must have set with no load or charge for a good while for the voltage to settle. So under what conditions are you measuring 12.1V? If you have the fridge and a few lights pulling power and read 12.1V then your batteries could be fine.

So before you get too worried, find a way to top off the batteries. Pay for a slip for a day or so to plug in.

[Jon Hacking]

I agree with the others, based on the data you've given so far. But you're right that batteries should last longer.

What voltage did you charge the batteries to?

You call them "GSM" batteries - are these the same as AGM? Although this whole business is an alphabet soup, GSM is a type of phone signal to me. The normal types of batteries (that I know about) are Wet (sealed or not), Gel, & AGM, with a few LiFePo (but they're very special cases). Wet cells are the most robust, & can take significant abuse, but Gel & AGM have special charging requirements. Specifically, if you take them to too high a voltage (which is temperature dependent) then you can kill them very quickly.

Taking 175Ah out of a 625Ah bank is bringing it down to 72%. A high quality deep-cycle battery should do that many times. But just for reference, we also have a 660Ah house bank, & only rarely do we take more than 100Ah out of it (but we have a large solar array to keep it topped up).

[Sandero]

We don't have good survey information from the OP. His monitoring may be out of sink.. his meters can be off. However... if practically speaking something like cabin lights are getting dim quickly it sounds as if the capacity is not there.

Charging of batteries with little capacity will see the voltage high and then drop because the batteries can't accept charge. They will measure full but they have little capacity.

I could be wrong and I usually am. But this is what it sounds like to me.

[Stu Jackson]

skipmac...what he said.

[skipmac]

One other comment. Looking into the Odyssey batteries I think these are AGM batteries (absorbed glass matt) which Odyssey web site refers to as acid starved.

Based on how I understand your charging routine this is very problematic for AGM batteries. They really need to be completely and fully charged on a regular basis or they can indeed die an early death.

To read a more complete discussion on AGM batteries and the issues with using them on a boat go to this link. AGM Batteries - Making The Choice - SailboatOwners.com

[exMaggieDrum]

I used to sell customers on using the battery percent of charge features on slick new monitors - until I went cruising full time and figured out it was more smoke than substance. They do have to be recalibrated often to be useful at all and you have to run the system through a special procedure to do that. And then it still isn't good info.

We just monitor volts and amps. If I suspect something is going on then I write down the stats on a regular basis to see. But if your batts are going down too fast for the same amp usage, then they are running out of capacity. Pure and simple. You may be able to get some back with the same batteries by equalization or or conditioning but you may not.

I trained my wife to constantly monitor the batteries - multiple times a day. It was easy as it was where we walked by many times a day and easy to read. We religiously avoided letting them get too low. They were Lifeline AGMs - 6v golf carts. They lasted well over 10 years full time cruising. But I never used the state of charge "data". I did make sure I did full recharges as often as possible. AGMs make that easier since they will take rapid charges quicker. Now I have big solar panels so hopefully the current batteries (on the new/old boat) will not have to be charged by genset or engine too much. But I will to fully recharge them if needed.

[Bernie10]

I havnt seen anything about charging voltage a 12 volt deep cycle battery needs 14 or 13.8 volts to be fully charged That's what I was told also at 11 volts your battery is considered flat.and double the didgets for 24 volt system pay to have your charging system tested. Cheers

[Sandero]

I second ExMaggie.... the hi tech monitors may be capable of interesting calcs about your batts... but they seem unreliable and require too much fidgeting to get useful data.

My Link 20 is very visible and I leave the display on volts and I can immediately tell what's up. The main bank 2 8Ds is on a couple of smallish solar panels as a trickle charge and it keeps them topped up nicely. The start is on an echo charge.

Occasionally I intentionally disconnect the Link and it resets... the volt meter readings appears to be accurate. I could care less about the other readings except amps when charging.

[ReMetau]

Have you checked the voltage using a good multimeter?

I had a battery monitor show low voltage on me, but I checked the batteries using a multimeter and all was fine. After some time, the voltage on the monitor started going up and down drastically in seconds from 12.5 to 11.0. Eventually I found that it was a loose connection in an in-line fuse to the monitor.

[a64pilot]

Before I tossed them I'd do what Lifeline calls a "boost charge"
http://www.lifelinebatteries.com/manual.pdf
They are of course another brand of AGM battery, and I have had exceptional luck with their aircraft batteries, they seem to know AGM batteries
Look at sections 5.1, 5.5 and 5.6 of the pdf


Sent from my iPad using Cruisers Sailing Forum

[Old Swampy]

I don't know about Odyssey and AGM batteries, but wet cells have to have electrolyte up above the plates. If it falls below the top of the plates, the batteries will behave like they have lost their capacity.