Batteries not holding Voltage

[Mike Banks]

Overcharging AGM batteries can dry the electrolyte out. I have on occasions added a little distilled water to each cell using a measuring syringe, to see if it makes any difference. Lotsa luck!.

If you wish to equalise the charge on all batteries, I just apply the unregulated power from some solar panels into the system--about twenty volts but very low amps so low heating effect. I have used this trick on old batteries to give them a bit of a jolt and equalise the cells.

My guess is over-charging. AGM's need LESS volts than do flooded lead-acid cells and particularly calcium types. If there is a rotten-eggs smell when you open a cell, that is a give-away sign of severe overcharging and a ruined battery, or damaged water-depleted electrolyte. The sulphuric acid itself is breaking down.

But as someone said--first call is to the manufacturer. If the batteries are under warranty, they may send a technician to diagnose the problem before you have to do anything by way of damage remediation.

[Cadence]

Load test them. A static voltage test shows about nothing.

[Stu Jackson]

Originally Posted by SV__Grace

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AGMs seemed like a good idea for cruising, but in reality they seem best if you have frequent access to shore power to get them to 100%.

Thx for that astute and correct comment. Maine Sail has been saying this for over a decade. AGMs are essentially worthless (compared to theri excessive cost) UNLESS they are recharged regularly, often, soon, repeatedly,... get the drift?


AGM Batteries - Making The Choice (from Maine Sail)

https://forums.sailboatowners.com/in...choice.124973/

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/in...teries.133773/

Additional Observations on the Limits of AGMs http://c34.org/bbs/index.php/topic,5....html#msg63004

[s/v Jedi]

AGM batteries are a good choice for starting batteries. When a large solar array gets the house bank in float every day, AGM can work well for house battery as well.

AGM loves float charge phase. LiFePO4 hates it.

[mitiempo]

I think they have been chronically undercharged. It is hard to over-charge a bank that size on a cruising boat, even if the voltage is a few points high.

The op hasn't stated how they are charged, how long they are charged for, and how often. Stu is correct that AGM batteries are fussy and want to be fully charged as often as possible. It takes a long time to fully charge the op's 850 AH bank.

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posted by SV Grace:

I'm pretty sure that I created the problem by not charging the batteries to 100% often enough. It just pained me to run the generator for 2 hours in bulk (@80 charging amps), 2 hours in absorption (@20 charging amps) and 4-6 hours in float (@8-10 charging amps) to get them to 100% but after I started doing so the batteries lasted another 2 years until I swapped them out.
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Batteries do not charge in float - well maybe if you have weeks to spare. Many chargers go into float way too soon. The batteries should be 95% charged or more when going into float - absorption after bulk is where the charging occurs.

[more]

AGM batteries are easy to kill while you are learning the ropes

[Quadrille in JB]

quote-AGMs seemed like a good idea for cruising, but in reality they seem best if you have frequent access to shore power to get them to 100%.-end quote

Correct me if I'm wrong, but my setup with 2-370W Sunpower panels with 2-100/30 Victron MPPT controllers charging 8-105 ah AGM batteries and a Victron 702 BM reach full charge each day. Usually when we get up the BM shows 90%-93% SOC. This is after running both a freezer and refrigerator and several fans and lights overnight. The BM shows a 100% SOC by noon, unless it is an overcast day which we don't have many of here in South Florida and the Bahamas.

I think solar charging with adequate capacity should be ideal for cruisers.

Bill in JB

[Emouchet]

Originally Posted by Quadrille in JB

Correct me if I'm wrong, but my setup with 2-370W Sunpower panels with 2-100/30 Victron MPPT controllers charging 8-105 ah AGM batteries and a Victron 702 BM reach full charge each day. Usually when we get up the BM shows 90%-93% SOC.
Bill in JB

You should carefully check the way you have setup your BM and your Victron MPPT working parameters. I strongly suspect they are considering your batteries to be full far too early.

By personal experience, it took me months to tweak the parameters of my BM and the MPPT controller, (all Victron) to work decently.

A quick dirty test: measure voltage and current at the battery post right around the time the MPPT says it switched from Bulk to Absorption. Most probably the voltage is not yet there. Same when it switches between Abs to Float. Use your own voltmeter. Do not rely on Victron reported information, for the sake of comparing.

On the MPPT, parameters such as BULK TIME LIMIT, ABSORPTION TIME LIMIT besides ABSORPTION VOLTAGE and FLOAT VOLTAGE as key numbers you need to play with.

On the BM, parameters such as TAIL CURRENT, CHARGE DETECTION TIME, PEUKERT EXPONENT, CHARGE EFFICIENCY FACTOR, TIME TO GO AVERAGING PERIOD probably needs some tune up.

Each time you tweak one parameter, avoid tweaking the other one at the same time. Observe a few days the change on the batteries. Take some notes. Repeat...

[Cheechako]

Did you let the batteries sit over night before testing? (isolated from each other) It sounds like you may have a shorted battery. It's not unusual, I've had a couple fairly new batts shorted over the years.

[more]

Originally Posted by Quadrille in JB

Correct me if I'm wrong, but my setup with 2-370W Sunpower panels with 2-100/30 Victron MPPT controllers

Please tell me how you put 2x 370w panels on your boat .i have lot bigger boat of your and have max 2x 150w solar panel and Victron 100/20 usually hard hit 20A charging.
now i see but 2 sunpower 370W panel have more m2 from your O'Day 34

[Quadrille in JB]

Emouchet,
Thanks for the input. When I installed the system I played with the parameters quite a lot but I've only adjusted the absorption voltage once. I haven't used my Fluke DVM but relied on Victron's reported voltage. I'll give it a try.

More,
I had an arch fabricated to my design to hold both the solar panels, the dingy, the radar, etc. by Joe Gooch of Riverside Marina in Ft. Pierce. It works out well and as you know you can never have too much solar.

[more]

Originally Posted by Quadrille in JB

More,
I had an arch fabricated to my design to hold both the solar panels, the dingy, the radar, etc. by Joe Gooch of Riverside Marina in Ft. Pierce. It works out well and as you know you can never have too much solar.

To big by my taste.

my 2x150w



lonely pictures

[Quadrille in JB]

More,
You have to sacrifice real estate for power.

[argonauta1]

AGM batteries are way too sensitive to less than an ideal charging cycle common to many sailing vessels. My first installation of AGMs was seriously unsatisfactory as they had to be discarded in just over a year, Henceforth, I stuck with either flooded or gells.

[markdj]

One thing that I have done since changing our batteries recently was to rewire them so that all heavy duty cables are the same length, this is challenging and does result in excess cabling but means that our 3x2 sets of batteries charge equally.

This article covers the reasons why, depending on the method of connection, could result in your centre batteries in the bank not being charged.

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Hope this helps.

We decided on the star formation with 2 new heavy duty busbars that all sets connect to +/-, and all wiring is the same length.