Battery SOC Low - Voltage Normal

[5erToyHauler]

Hi All.

I'm new here so go easy on me. I've Googled for hours but can't find any solid answers. My setup is in my signature. So here's my issue....

Whether plugged into shore power, running my generator, or charging with my solar setup under the sun on a good day, I can't get my SOC up on my batteries. I'm monitoring my vitals through my display/meter for my solar setup. When we were out boondocking 2 weekends ago, I couldn't seem to get my batteries up past 60%. I could run my generator for many hours. It would only bring them up to the low 60's and than hover there. With the generator running, the SOC would drop when using lots of 12v power. Not by a lot but it would drop. I will note that the converter was working. During the day when the panel was charging at 10-16amps it would bring the SOC up to the 90's. But as soon as the sun disappeared it would drop back down to that 58%-61% range. Here's the kicker, my battery voltage readings seemed to be dead on. Exactly what they were last season when my solar display would show my batteries charging right up to 100% and staying there. There is no abnormal drop in voltage (according to my display) when 12v power is being used. I can't say that I've experienced any noticeable loss in capacity. The furnace ran all through the night. The batteries were drawn down in the morning as per the norm. Than they charge back up to the recent norm of 58%. I can't get them to show past 61% no matter how long the generator runs or the shore power is connected. And again, when the solar panel is going strong it will bring the SOC up into the 90's. But once the sun goes away it will go back down around 58%. My best guess would be that the converter can't get the high SOC readings because of the low amperage it charges at compared to my solar setup. All voltage readings on my display seem to match the numbers I get when taken directly off the batteries using my multimeter. Last night I went and checked out my readings again. The trailer had sat in good sun for a few days with the main battery disconnect off. My display was showing 94% SOC @ 13.0V. When I turned the main power disconnect to "On" It went down to 78% SOC @ 13.0V. There would be next to nothing for load at this point. I turned my kitchen lights on and it went down to 50% @ 12.8V. Shut them off and I went to 58% @ 12.9V. Than I cut the main disconnect and things stayed the same (58% @ 12.9V). SOC never recovered more than that.

So it seems that once a load is applied, the SOC/ Capacity doesn't hold up but the voltage stays where it should. In my research the only situation that I could come up with was that I may have a case of Sulphation. My Solar Charge Controller has multiple stages of charging. It is supposed to equalize when necessary. How it knows when to do so...... I am not sure. If my voltage was dropping and the batteries were draining quickly than it would be an easy diagnosis. But, the fact that the voltage seems to fluctuate on a normal scale while the SOC is all over the place, has me scratching my head. So I'm calling out all experts to see what gives?

Thanks in advance for your help.

[consumeratlarge]

I would check water, separate the batteries, and try all of that again, one at a time, to find the bad battery. BTW, 13v is higher than a full battery at rest should be, right? I though 12.7 or so is fantastic. But, if you're noticing a bigger voltage sag under a load than usual, something's not right.
Maybe your % of charge is based on having a charge hitting it. Voltage only reading to indicate state of charge requires disconnecting charger and load for something like an hour. If you find a battery with a bad cell, you can try zapping it with an equalizing charge, which is just a higher charge, like 15v. Then run that battery down and do it again, it just may bring the low cell up, but it's kind of a slim chance. I always try the pulsing, desulphating charger, too, which is also a slim chance, but has worked to give longer life to an uneven battery. Be sure to add water after several equalizing charges, since it will gas it out during the process.

[MEXICOWANDERER]

Your meter showing state-of-charge could be off-it's-rocker.

Use a hydrometer to see where the batteries are really at charge wise. Meters are as reliable as using a Fortune Teller. A hydrometer dip will indicate if any of your cells need equalization.

[westend]

Symptoms are typical of a failing battery cell. The voltage will appear to be normal until a load is placed on the batteries. The load will then expose the lack of voltage from the missing or failing cell. One clue to this may be that you can only charge the batteries to 94% with your solar and no loads present. The solar should attain 100% charge in a few days.

Have you checked the batteries with a hydrometer recently?

[Dick_A]

Moved from General RV'ing forum.