Battery Question

[Kammy]

I have 2-12v AGM 100 amp. Interstate Batteries in my 27' Class A Winnebago Sightseer, they are about 3+yrs. old and decided to retire. I tried dry camping recently and the batteries dropped from 13.72 to 10.75 in a matter of three hours.

I had the batteries load tested three times in the last year and every time they came up perfectly fine. I do not recall any time that I have depleted the batteries severely.

I thought that AGM's were supposed to last longer than that. I assume that they are due to be replaced??? I like the maintenance free aspect of AGM's but I would like a longer life expectancy.

Amy ideas why they would fail after only three years!!!!

[DriVer]

Originally Posted by Kammy

Amy ideas why they would fail after only three years!!!!

Do you have an intelligent charging system?

[RV Wizard]

Did you check to see if there was a significant load on the bank during the three hours you noticed this voltage drop? If there was no load, then I would also lean toward the recharging voltage and current rate to be the culprit of damaging the batteries.

[wa8yxm]

[QUOTE=Kammy;741829
I thought that AGM's were supposed to last longer than that. I assume that they are due to be replaced??? I like the maintenance free aspect of AGM's but I would like a longer life expectancy.

Amy ideas why they would fail after only three years!!!![/QUOTE]

Well, that is what they claim.. But you are not the first person I have heard from who had AGM's go and go bad, and do so both suddenly and fast (I AM) and I charge mine with a Xantrex Prosine 2.0 which is one outstanding intelligent charger. Alas, I can not afford replacements any time soon.. Thankfully they are not the ONLY batteries in the coach. I just re-configure and can use a pair of Interstate U-2200's for the inverter too... I now have it so I can survive from 11pm to 8am with only battery power.. But to do so I have to kill the inverter and all other optional loads. (Just run the furnace)

[BryanL]

3 years is a bit on the short side for an AGM that is properly used and maintained.

reasons for a shorter life than expected include small odds of a battery failure (plate short or some other type fault), sitting too long without any maintenance charging, non-optimum charging voltages, insufficient charging, excess deep cycling, heat, ...

reasons for a misleading voltage reading include not allowing the battery to 'rest' with no charge or discharge for at least a half hour, poor connections, a test point that has other metals between the DVM and the battery terminals, ...

AGM's have low self discharge rates but will still age rapidly if left sitting for months. Battery storage maintenance is often overlooked for RV's that spend a lot of time between uses. A good maintenance device will not only keep the charge up but will also do something to inhibit sulfation.

It is good to find out why battery life is not satisfactory so you can fix the underlying problem. Too many just go out and buy more batteries and that doesn't usually solve the problem.

[GaryKD]

Hi Kammy,
Welcome to iRV2. Be careful of the auto parts store that claim they can load test batteries. I took several of my batteries to 3 different places and got a wide variety of answers. Finally, I went to my trusty AC Delco battery store and they found one battery bad.

Like previously posted, the drop in voltage over the time mentioned is due to:
1. load
2. charge
3. bad battery(s)

Before you take the batteries for load test, make sure they are as fully charged as they can be. Then take the batteries to a trusted source for load testing. I have found NAPA stores and those auto parts stores specializing in batteries to be a good source for load testing. Also, be careful if the person assigned to do the load test seems to be the part time kid who may not know what he/she is doing.

Can you give us additional help by letting us know about the possible load on the batteries and how you know they are at full charge? Lastly, how quickly did the batteries come up to full charge from the discharged sate in your OP.

[Kammy]

Originally Posted by GaryKD

Hi Kammy,
Welcome to iRV2. Be careful of the auto parts store that claim they can load test batteries. I took several of my batteries to 3 different places and got a wide variety of answers. Finally, I went to my trusty AC Delco battery store and they found one battery bad.

Like previously posted, the drop in voltage over the time mentioned is due to:
1. load
2. charge
3. bad battery(s)

Before you take the batteries for load test, make sure they are as fully charged as they can be. Then take the batteries to a trusted source for load testing. I have found NAPA stores and those auto parts stores specializing in batteries to be a good source for load testing. Also, be careful if the person assigned to do the load test seems to be the part time kid who may not know what he/she is doing.

Can you give us additional help by letting us know about the possible load on the batteries and how you know they are at full charge? Lastly, how quickly did the batteries come up to full charge from the discharged sate in your OP.

My Motor Home is set up with two solar panels of 160 watts and 165 watts with a Blue Sky Controller. The batteries read 14.02 throughout the day when the sun is shinning. They read 13.5-13.75 when the sun goes down and I am hooked up to shore power.
What I did was shut the shore power off to see if the batteries would run the furnace during the night.(They were at 13.7 when I shut the power off). The only other thing that is on is the refrigerator which when not plugged in to electricity runs off propane, granted it has some electrical parts which draw on the batteries. I do not have an inverter in the RV.

The load tests were done by La Mesa RV in Yuma, Camping World, and a Winnebago dealer in Green Bay. The last load test was done on November 23, 2010 by La Mesa RV in Tucson when they checked out a furnace problem I was having.

The batteries come up to charge quickly when I plug back into electricity, i.e. 13.4-13.7.

When the RV is a home I leave it plugged in. It gets occasional use when at home. We travel about 6 mo. out of the year with the RV.

[TQ60]

Ok, they are at 13.72 and drop to 10.75 in 3 hours, they also come up real fast.

Let's talk "glass of water" to see what is happening.

If you use a tablespoon to fill a glass, it takes a certian amount of time to fill and if you use same spoon to empty, it taks a given amount of time.

Now 1/2 fill same glass with sand, less time to fill and less time to drain.

If you are floating at 13.75 it is ok, should be 13.5, but if you are dropping to 10.75 you are getting close to the lower limit.

Also, if the label states 100 amp hours, this is at the 8 hour rate, so 12.5 amps is the expected load.

As the load per string or battery goes up the capacity goes down.

Get the exact battery part number and check the web for the spec sheet, you may find that your battery output is less than you expect based on the current drain.

AGM batteries do not like to be stored without a trickle charger, they prefer to be float charged with the current not to exceed 1% of capacity, so if it ia a 100 amp hour battery they do not exceed 1 amp float charge.

Also insure voltage does not exceed 2.25 volts per cell or 13.5 VDC while floating.

Load tests are not real good as they are short durations, the lesser capacity of a sulfated battery will still pass most tests.

[BillJ999]

There is a video on the Optima site which deals with this subject. Take a look at Tech Tip #2 here:

Optima Battery Product Support - Tech Tips for Optima Batteries

They state that their AGM batteries last an average of 6 years.

[Wanabee FTer]

Originally Posted by Kammy

My Motor Home is set up with two solar panels of 160 watts and 165 watts with a Blue Sky Controller. The batteries read 14.02 throughout the day when the sun is shinning. They read 13.5-13.75

How far away from the batteries is the charge controller mounted, and what gauge wire was used for the install?

[GaryKD]

Hi Kammy,
The 13.7 VDC reading was not a "real" reading. Once the charger is disconnected, one needs to let the batteries sit for a couple of hours. Then take a reading. AGMs fully charged is 12.8 VDC. I'm not sure how much the furnace ran, but the furnace is a really big draw on the batteries.

When you get a chance, fully charge the batteries and let them sit, with no load on them. Over the period of one month a self discharge rate of 1 to 3% is acceptable. If the batteries self discharge more than that they are just wearing out. If they significantly discharge more than that, there may be something wrong with one of the batteries.

[Kammy]

The controller must be within about a foot to a foot and one half. The batteries are located under the steps and the controller is located just inside the door on the side of the counter. From every thing I have read this is excellent. Just a note: I am leaning toward a wiring problem with the wiring being to small to get the solar power to the batteries. Also the Blue Sky Solar Boost 2000e controller is only a two stage controller. I plan to have a three stage controller installed along with a good battery monitor and having the solar system rewired with heavier wiring where appropriate (panels to controller{6 gauge}-controller to batteries{4gauge or 2 gauge).

[Wanabee FTer]

Hi Kammy,
It sounds like you are thinking the same thing I was thinking.
The Solar installation may be sub-par.
Comparing the battery state of charge to filling a glass of water, the glass might be starting out only 1/2 full. This would cause what seems like a rapid discharge of the battery. Perhaps you have already found Handy Bob's Solar page. Lots of good info there.

[TQ60]

At 165 watts we are talking about 12 amps of current if voltage is 13.5.

12 amps of current can be safely carried by a #14 wire, so a #12 would be fine for each panel system, this would handle 20 amps each.

I would suggest running both hot and return wires directly from each panel to the controller, and also using soldered connectors instead of crimp on type, grease all connections.

Given the short length (less than 30 feet) there is little need for larger wire as the voltage drop is minimal, #10 would be the largest I would use if you want to get bigger.

Now back to the batteries.

Regardless of the capacity of the battery, as long as the cells inside the battery are not open, leaky or shorted the fully charged voltage will be the same regardless of degradation so leaving the battery sit to later measure the voltage is of little value.

The main clue here is the rapid recharge, this indicates a smaller capacity, (see above post with glass demonstration).

Now, of the many ways to test batteries with multiple devices and procedures, there is only ONE way to correctly determine if the battery is actually GOOD.

Before everyone screams about their favorite testor read on.

MOST devices like load testors, conductance and other magical devices can tell that a battery is BAD, they also can indicate that the battery LOOKS LIKE A GOOD ONE, but NONE can state that the battery is good.

Now, the only way to state that the battery is GOOD is to be certian that it will supply a specified current for a specified time and maintain a voltage above a specific point.

Before I go long in details there is another issue regarding AGM batteries.
They are designed as stationary power for backup operations. The intent is to be installed inside a controlled environment with ambient temperature between 65 and 75 degrees. They also do not like deep discharges, or multiple cycles, usually about 1000 charge/discharge cycles are what they are rated at. The lower limit is 1.75 VPC, go lower and this can damage the cell. The design is for a 10 year installed life under the above limitations. Over these 10 years they will have "age degradation" where the plates loose the ability to do their job, the speed at which the battery ages is determined by how the battery is treated. If the battery is in high temperature above 90 degrees it can reduce the lifespan of the battey. Freezing is not so good either, but the damage may not be as bad. So if you have AGM batteries installed in a spot that can get hot due to engine heat or outdoor heat, and you are operating off grid where the batteries may be discharged near or below 1.75 VPC due to no low voltage disconnect system, and if this is done 6 months out of the year, then depending on how many cycles are being used the batteries may only last 3 to 6 years on a good day.

Here is the long explanation on how to test yours for capacity.
So, if we have a 100 AH AGM battery as stated on the label, the small print will likely state 97 AH @ 8 hour rate.

We do the math and find that 97/8 is 12.12 amps.

The voltage used to determine a depleted battery is 1.75 Volts Per Cell, so a dead battery is 10.5 vdc.

If the above battery is fully charged then a 12 amp load is applied, it should maintain a voltage above 10.5 VDC for about 8 hours.

If you have an amp meter you could experiment with headlights or other devices to build a load, I think a dual filiment bulb could be configured to get a 12 amp load. Either by connecting one or the other filiment, or both in parallel or series one could get any of 3 different loads.

If you have a smaller load then the rate should be about the same, divide the size of the battery by the load to get the run time.

If you have a larger load then all bets are off as the internal resistance of the battery reduces the output of the battery, so a 50 amp load will NOT run for 2 hours, a 50 amp load will likely run for about 1.25 hours, one needs to look up the battery data sheet to show what the battery output would be.

Now you can actually test your battery with simple devices, a meter and a light bulb, and you can determine exactly what the capacity of your battery is.

Next is measuring all of the loads and charging systems to insure the batteries are being treated as they should and one is not expectig them to perform better than they are capable of.