Battery and the cold question

Hi all, 

The AGM 200 ah battery in my van (the "house" battery, not the engine battery) is showing 57% charge according to the battery monitor. It's been that way for days. It's charged by two 100w solar panels, as well as the engine. Neither seem to be raising the percentage charged. Stuck solid at 57% despite driving around quite a bit the other day.

I'm hoping it's these cold temps were seeing here in Western NC. The only thing drawing on it is the charge controller that I can tell. Everything else (inverter, lights, fan) is off.

Any thoughts? Anything I should do? Just wait until it warms up?

How old is the battery?

If I had a battery charger, I would hook it up and plug it in and see if charging it for 12 hours or so had any effect.

Just over a year old. I'll see if I can find a battery charger. I was thinking the solar panels were acting as a battery charger is the reason I haven't tried that. But maybe on these short days it's not getting much juice from the panels. 
 

The voltage does read 13.8, it's just the percentage charged number seems stuck at 57%.

I'm a bit of a luddite, but I've never trusted anything other than a hydrometer to tell me a state of charge.  

Yeah it sounds like a battery monitor problem rather than a battery problem...can you reset the battery monitor?

In reply to Streetwiseguy :

Hydrometers won't work on AGM batteries, unfortunately. 

I agree with resetting the battery monitor. 

Volt meters don't often lie...

Is the 13.8 in the battery or is that power from the solar?

Don't those battery monitors just go off of voltage?  Otherwise, would it being doing some sort of occasional load test?  I kind of doubt it.

If so, clearly a monitor issue.

13.8v seems very good.  Is that after it sat without any charge for a while?

Yeah 13.8 yesterday before any driving and without much sun.

@bentwrench, not sure what you mean, it's solar panels connected and charging a battery.

Ill see if I can reset the monitor. When I unplug it and plug it back in it goes right back to where it was. Must have some sort of memory.

This is what the monitor looks like now. Seems like it should be at 100ish percent given the voltage is 13.8. I'm going to recalibrate it if you all agree.

Is that 13.8 volts the reading with it attached to the solar charger? I wonder what voltage it would read if it was disconnected for an hour. That might be informative. 

In reply to Floating Doc (Forum Supporter) :

Yeah, that's attached to the solar charger. That's an interesting idea. I might try that. Thanks!

Edit: Thinking more about it, wouldn't that be the same as checking it in the morning?

I disconnected the solar panels and the battery went down to 13.0 volts after an hour. It's a sunny day here and the battery was at 13.8 before I unplugged. This all according to the monitor. 
 

Does what I just shared seem healthy?

CyberEric said:

I disconnected the solar panels and the battery went down to 13.0 volts after an hour. It's a sunny day here and the battery was at 13.8 before I unplugged. This all according to the monitor. 
 

Does what I just shared seem healthy?

Voltage with the panels attached doesn't tell you anything about the battery health.  To charge a battery you need to raise the voltage above what it would put out by itself to force the reactions to run in the other direction.  Lead acid with six cells (nominally 12V) tops out about 12.8, so that 13.8 is what the charge controller is putting out using the solar as input.

Are you running anything with the battery, or is it just sitting there?  200 watts of solar panels should be way more than the self discharge rate and able to get it up to full charge from zero in a few days to a week, so if it's been stuck at 60% then something is wrong, either the monitor circuit, the charge controller, or maybe the panels are just covered in something.

It's mostly just sitting there right now. I turn on the lights occasionally. We aren't living in the van at the moment, so it's not being used a lot. This is a Renogy 12V Deep cycle AGM 200 ah battery, by the way.  

The panels are clean (just checked). The charge controller seems to be working (green light is blinking). 

Like aircooled mentioned above, I'm thinking that the battery monitor just needs to be recalibrated. Renogy indicates that the monitor needs to be recalibrated at times.

But I could be wrong. I don't know how the monitor calculates the percentage of charge. 13.0 seems pretty good to me for having no power coming in for an hour. According to this website, that's well above fully charged.

Does anyone know anything about how battery monitors calculate percentage charged, especially the Renogy unit I have?