AGM Battery Capacity?

[woodhog]

I want to measure the capacity of AGM batteries, I have monitoring
equipment in my camper, Trimetric monitor.

However that only reads the voltage as my solar charges the system and then as the voltage goes down during the night.

What can I do to find out how long my batteries are going to last as they age and eventually will need to be replaced, the only indication
I had for the last set was when the fridge (DC compressor type) would no longer run all night.. when they were new batteries, the fridge would easily run all night.


There must be some way to tell how much life is left in them rather than wait for the fridge to fail again ??

Meter of some kind ???

[woodhog]

pnichols wrote:
Just as a side note ... rate of change of state-of-charge as you're using a battery versus it's capacity are very much related to each other.

That's why I finally got rid of our last set of RV batteries. Their state-of-charge was dropping too fast when we were camping as compared to when they were new ... which meant that their capacity was no longer what it was when they were new.

That is what happened to us also, same thing.. they charged up to the same voltage as always but discharged much more quickly..

Thanks

[pnichols]

Just as a side note ... rate of change of state-of-charge as you're using a battery versus it's capacity are very much related to each other.

That's why I finally got rid of our last set of RV batteries. Their state-of-charge was dropping too fast when we were camping as compared to when they were new ... which meant that their capacity was no longer what it was when they were new.

[MEXICOWANDERER]

The discharge characteristics of a battery in a range of 50% SOC to 0% SOC tells the story regarding capacity and remaining LIFESPAN of the battery. State-of-charge and battery capacity are as different as road apples and cow pies.

[Chris_Bryant]

Almot wrote:

Chris Bryant wrote:
All of the AGMs tested 100%, and had the spec'd resistance, after over 6 years of heavy use.

If this tester shows that battery didn't change resistance after 6 years of heavy use, I wouldn't trust it.

I wonder what Mex would have to say on these miracle devices.

It has tested many other batteries apparently accurately, and it did give the resistance that Full River gives in their specs, plus anecdotal evidence- owner reports the same run time he has had.

I think having a good charger made the difference- charged at a fairly low rate (150 amps, but 1100 amp hours of capacity, plus 850 watts solar), charge parameters set at Full River specs- temperature compensation, etc.

[Almot]

woodhog wrote:

Will the Trimetric come up with similar results if I can figure out
how to program it at another level, mine is L1 at the moment.It is a 2025.

Are all three measuring the capacity left in a battery that is not new?

Battery monitor will provide more-less accurate estimate for SOC only. Doesn't matter whether old or new battery. It simply counts amp-hours in and out after you've fully charged it and reset SOC to 100%.

To program the Trimetric, you need to install the shunt. Then follow the manual.

Looks like you've been using an expensive monitor as a simple volt meter that you could've bought for $10. Btw, I don't have battery monitor and don't feel like I need it - despite the fact that my batteries are AGM and therefore have no direct way of measuring SOC. Big solar, low loads, batteries are fully charged by noon or early afternoon.

[MEXICOWANDERER]

Concorde LIFELINE has a FREE AGM manual online to download.

It lists an exact method*, and recipe to determine battery CAPACITY meaning available kWh of the battery at maximum storage. It's like maximum RPM or miles per hour in a car. It is absolute. Unless you lie, cheat or allow yourself to be cheated.

I wrote long ago here on this forum about HOW HARD it is to determine an AGM battery's TRUTHFUL state of charge along with how hard it is to get a grip on the DEGRADATION either through misuse or age of a VRB (sealed battery).

A simple wall meter does not cut-it. Because no "affordable" amp hour meter I know of has kWh capability, in a capacity = a large battery. Even with kWh a person has to LEARN the significance of what they are reading.

I'll give you an idea. My laptop. 90% battery time remaining, is almost accurate 50% time remaining makes my eyes roll. 30% time remaining is a cruel joke - I have MINUTES to plug in or shut down. Get the drift?

[Almot]

Chris Bryant wrote:
All of the AGMs tested 100%, and had the spec'd resistance, after over 6 years of heavy use.

If this tester shows that battery didn't change resistance after 6 years of heavy use, I wouldn't trust it.

I wonder what Mex would have to say on these miracle devices.

[woodhog]

Chris Bryant wrote:
A while back I bought this battery tester , which measures capacity using internal battery resistance.
FWIW, seemed to work fine on the AGMs I tested it on, and a couple of regular flooded batteries. Gives capacity in percentage.
All of the AGMs tested 100%, and had the spec'd resistance, after over 6 years of heavy use.

This seems to be what I was thinking about when I posted...

I looked around after seeing the above and also found this one:

capacity meter ? Are these two
meters operating the same way, designed the same?


Will the Trimetric come up with similar results if I can figure out
how to program it at another level, mine is L1 at the moment.It is a 2025.

Are all three measuring the capacity left in a battery that is not new?

[CA_Traveler]

Has anyone used the above tester on 2x6V in series? The manual is 12V singel battery focused. Also wondering about series/parallel house batteries.

[Chris_Bryant]

A while back I bought this battery tester , which measures capacity using internal battery resistance.
FWIW, seemed to work fine on the AGMs I tested it on, and a couple of regular flooded batteries. Gives capacity in percentage.
All of the AGMs tested 100%, and had the spec'd resistance, after over 6 years of heavy use.

[EsoxLucius]

12.1 volts instead of 2.1 volts?

Thanks for the edit, I was confused.

[pnichols]

I have had AGM batteries in our RV for about 8 1/2 years. The first set for 8 years and our current set for 6 months.

I watch their voltage to tell how low their charge is. I turn everything that they power OFF for a few minutes - or at least turn OFF the big current draw items (a compressor type refrigerator is a big current draw item) for a few minutes and then check the voltage they're delivering. It this voltage reads around 12.1 volts, it's time to get them on a charger. Granted this does not tell me their capacity over time, but it tells me not to push them much farther without getting a charger on them pretty soon.

On my first set of AGM batteries that I replaced after 8 years, over time I learned that as the years went by they seemed to run down to around 12.1 volts sooner than they used to. Near their end, the time for them to run down to 12.1 volts was getting too short for me to want to bother with recharging them that often. This was how I kept an eye on their "capacity" once I got used to how they acted as we camped.

[Almot]

landyacht318 wrote:
Capacity test.

Divide listed amp hour rate of battery bank by 20.

A 100 AH battery can power a 5 amp load for 20 hours before voltage drops to 10.5v.

This is why I don't recommend the OP doing it. He needs to understand what he is doing, and how. The battery is AGM. Those typically have higher voltage at any given SOC. Trying to discharge it down to 50% - following the chart for regular wet battery - you will discharge it much deeper.

The result - incorrect estimates for capacity, and potentially damaged battery.

[landyacht318]

Capacity test.

Divide listed amp hour rate of battery bank by 20.

A 100 AH battery can power a 5 amp load for 20 hours before voltage drops to 10.5v.

Apply a steady 5 amp load with 100AH battery at 77F and see how long it takes voltage to hit 10.5v.

18 hours? 14 hours?

Infer remaining battery capacity by how long it takes for voltage to hit 10.5v.

Halfass capacity test.

Apply steady 5 amps load on 100AH battery for 10 hours at 77f. Remove load, Watch how quickly and how high voltage rebounds.

Quick rebound to ~12.2v, and Whohoo
Slow rebound to 11.92v and BooHoo

Once you guestimate totah remaining AH capacity, be sure to change this setting on Trimetric.

Recharge batteries at 77f at 14.4v until amps taper to 0.5% of total capacity.
Reset trimetric.