battery capacity issue

[townline]

I have a new 100amp agm battery duracell hooked up to a renogy 200 watt system.
 there is also a amp draw  moniter. From full charge at night say 12.75v, i use 1.0 amp
per hour for 10 hrs battery goes down to 12.1 volts.This is the 2nd battery i got from
batteries plus and actually seems better than the 1st one i returned. I am also letting
 the battery rest after turning off load to get accurate reading. duracell and batteries
plus are not helping me.

 

[XERTYX]

I'm not an expert but the state of charge chart I use on my small AGM system states that 13.0v is full charge 12.75 is 90%. It sounds like you're not reaching a full charge and your battery is being consistently under charged. What float voltage do you use on your charge controller?

 

[XERTYX]

As an example on my small system I have a $10 chinese charge controller. The displayed voltage when its low is off by about a tenth of a volt. At full charge it seems to be accurate so I set the voltage to 14.3v rather than 14.4v for a little insurance.

 

[townline]

Was being conservative on stating12.75v The float is 14.4 and it goes there. I have .1 v discrepancy between my multi meter and amp meter.
The rover li 20 is at sealed setting and battery has never been over charge or drained.

 

[XERTYX]

Isnt AGM considered GEL not SLA (sealed lead acid) I looked at the specs on the renogy site. I want to say I have mine set as GEL. Maybe its using the wrong algorithm to charge it? Just spitballing.

 

[XERTYX]

The only other thing I can think of is when I built my first solar system years and years ago. I bid-sniped some 10w panels on ebay but could never seem to snag a charge controller.

So I used the panels without one and kept and eye on them trying not to overcharge the used AGM batteries. Eventually their capacity was for crap and I read online that overcharging an AGM causes the glass mat inside to dry out when the electrolyte boils and that section of mat will never absorb electrolyte again.

But if yours arent overcharged I cant imagine why the glass mat would have dry patches.

 

[highdesertranger]

Voltage is a poor indicator of State of Charge(SOC).

An amp counter that counts and logs amps in and out is much more accurate.
Does your amp counter count and log amps in and out?

This time of year you have much longer than 10 hours between max charge. Closer to 16-20 hours depending on location.

how many amps is your solar producing and for how many hours?

highdesertranger

 

[jonyjoe303]

are you measuring the voltage off of the battery terminals while charging?
You have to have 14.4 volts at the battery terminals for several hours to fully charge, some charge controllers go to float too quickly. 
I suspect also the battery is being undercharged. It happened to me too. Once it starts losing capacity it reaches 14.4 volts too quickly (surface voltage) and will have maybe 30ah capacity for a 100ah battery.

I would check/doublecheck voltage at terminals while charging. Every single controller I had pwm or mppt has been at least .5 volts off from what the battery terminals read. At controller 14.4 volts, the battery terminals were at 13.9 volts, the battery was never getting a full charge.
Don't bother rewiring everything with larger gauge wires, if your controller has the option to increase the bulk voltage that the easy fix. I tried rewiring but you can only put a certain gauge wire on the controller, it won't take massive 6 gauge or higher wire that you might need.

Don't worry about overcharging your agm especially with a 200 watt solar system, thats trickle charging for such a large battery, most agm's can handle up to 14.7 volts but check your battery manual for max voltage. Undercharging is what will destroy an agm.

 

[future_vandweller]

I have a new 100amp agm battery duracell hooked up to a renogy 200 watt system.
 there is also a amp draw  moniter. From full charge at night say 12.75v, i use 1.0 amp
per hour for 10 hrs battery goes down to 12.1 volts.This is the 2nd battery i got from
batteries plus and actually seems better than the 1st one i returned. I am also letting
 the battery rest after turning off load to get accurate reading. duracell and batteries
plus are not helping me.

As others have pointed out, battery voltage is not a reliable indicator of its charge state. In addition, a charge controller does not know the battery voltage if it is actively (bulk) charging the battery.  The reason for this that there's a voltage drop on the wires from the controller to the battery and this voltage drop depends on the current being delivered to the battery.  A good charge counting battery monitor is the only way to accurately track a battery's charge level.  Many battery manufacturers also recommend returning 10-15% more charge to the battery than was taken out during the previous discharge, to account for inefficiencies in the charging process.