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Old 05-19-2011, 12:40 PM   #1
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Evergreen , Colorado
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Bad Batteries?

I have 2 group 27 interstate deep cycle batteries in our 2008 airstream international 23D. I bought the unit this winter from California, and the guy I bought it from babied the unit in general. I have to assume the batteries are original. Also I replaced the original converter with Intelipower PD4655 2 months ago.

Here's my issue. It seems like the batteries are draining a lot faster than they should when boondocking. I am also getting strange readings on the monitor panel, but more on that in a minute. Here is what I have done so far to test:

1) Charged the batteries to full via shore power. Took a reading a volt meter with the batteries disconnected. Each reading 13.6 volts immediately after charging or so (maybe a bit higher - cant recall)

2) Left the batteries disconnected and waited 36 hours. Tested again, and batteries tested at 13.2 volts. Strage - seemed high as I thought they should drop to 12.6

3) Put them under load (24 interior halogen lights running for an hour). Tested the battery again (diconnected) and they were reading 12.6 volts

3) Connected batteries, charged up overnight via shore power

4) Tested batteries in the morning - reading 13.2 volts or so.

5) Turned on 13 halogen interior lights, furnace (set to 68 degrees in 46 degree weather currently) and water heater. also ran the water pump for a minute or so. Trying to simulate typical evening use this time of year. Left the all on for 2 hours.

6) Turned everything off except the monitor panel and tested the batteries while still connected. Got a reading of 12.2 volts.

Also - before turning everything off, I checked the monitor panel and it said I had 1/2 battery left! I tested the batteries while everything was running too and I got a reading in the mid 11's Then I turned everything off, and the panel jumped up to 3/4 full.

What the heck is going on?? Any ideas? I suspect my batteries are bad.

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Old 05-19-2011, 01:04 PM   #2
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Hi, the batteries in my trailer seem to last about three years; I have replaced them twice so far. Never trust your monitor panel especially for the batteries. The panel is programmed to read 7/8 at the highest while on shore power.


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Old 05-19-2011, 03:02 PM   #3
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Take the batteries to a auto parts store and have them load test them....they can put a higher load on them.
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Old 05-19-2011, 03:11 PM   #4
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I'm with Robert

Originally Posted by Nightwatch View Post
I have 2 group 27 interstate deep cycle batteries in our 2008 airstream international 23D. I bought the unit this winter from California, and the guy I bought it from babied the unit in general. I have to assume the batteries are original. Also I replaced the original converter with Intelipower PD4655 2 months ago.
.............. ............
What the heck is going on?? Any ideas? I suspect my batteries are bad.

Ive seen where the "monitor panel" was not so dependable as well. I would use a meter and compair. You may find a consisitancey in the numbers. It has been awhile since I did it but I think it was something like the monitor was accurate while the battery was high and low but was a little off while in the middle.
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Old 05-19-2011, 04:12 PM   #5
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Batteries; A mystery

Get a hydrometer and read the specific gravity of the electrolyte. It will read 1260 if the battery comes back to a full charge. I would think 3 years is about the life span of the batteries; especially when they set unused for long periods of time.
I have batteries in my farm tractors that are 14 years old and still start the tractors when needed. They get used on a somewhat regular basis; I also have batteries that only last a couple of years in other equipment. Can't explain why there is such a big difference in the life span.
The battery that came in our riding mower lasted 10 years; I replaced it last year and this year the 1 year old battery was dead. ?????
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Old 05-19-2011, 04:48 PM   #6
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The battery monitor is worthless, don't use it.

The voltage readings are not unusual except for the last readings showing 12.2 volts and 11 volts which would indicate nearly full discharge.

The batteries are probably shot due to age etc. 4 years is a pretty good run though some people do get a little more time from them. Lots of things shorten the life, overcharging, deep discharge (especially if the battery stays that way for a long period, anything over a few hours is increasingly bad), low water, heat.
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Old 05-19-2011, 07:04 PM   #7
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This is one reason I went with a solar panel to keep the charge up on my batteries. So far I am very happy with the results.

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Old 05-23-2011, 11:12 AM   #8
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All measures need to be properly considered for a proper interpretation.

The usual OEM battery monitor is a very imprecise item useful only as a general indication.

Specific gravity is old school and not worth the risk as far as modern battery maintenance goes. It doesn't tell you anything a proper voltage measure will also provide for RV battery needs.

Load testing and such things are also really not necessary as your experience in actual use should be able to tell you everything you need to know.

The voltages measured in the OP sound about right. 13.2 after a bit of charging is measuring the surface charge. Pulling on that with several amps for an hour gets it down to nominal full charge voltage by removing that surface charge.

Note that the batteries are rated at about a 120 watt load for the pair. When you pull more than this, you can significantly reduce available capacity (about 12 usable watt hours per pound of battery). This is what 'use profile' is all about. Watching how battery voltage drops and recovers from significant loads will tell you a lot about the current battery condition and age.

A couple of caveats: one is to not get overzealous in battery measures. You can get more than a 10% variance each from factors such as temperature, age, cycle to cycle variance, and use profile. Thinking you can get any measure of battery capabilities down to a gnat's eyelash is a fool's errand.

Another caveat: always let the battery rest for at least a half hour of no significant charging or discharging before using voltage measures as that will make them easier to interpret.

Solar is nice but there really isn't room for an adequately sized solar system on most Airstream TT's. They don't provide enough current for vigorous battery charging that stirs up the battery and few controllers provide any sulfation inhibiting technique.

It will take 8 hours or more to fully charge a lead acid battery. The converter you have should do a good job at this, especially if it is allowed to maintain the battery during storage (I think it is a 'charge wizard' type).

Out in the field, just keep an eye on voltage when things are quiet - the furnance hasn't been running, the water pump hasn't been in use, and there isn't any use of lights or other such loads - When the voltage gets below 12.4v in these conditions, start to plan a recharge sometime when convenient. When it gets down to 12.2v put some priority on recharging. If it gets down to 12.0v, recharge now.
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Old 05-23-2011, 01:58 PM   #9
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Ditto on "bryanl's" comments. Battery voltage is a poor indication of condition, as it fluctuates depending on conditions at measurement. That is why the battery (autoparts stores) measure current under simulated load.

It sounds like your batteries are handling the load normally. The real test is how they last while dry camping. I'd see how they hold up under actual conditions. If you can go several days with moderate use, they are OK. (By the way, even new batteries won't last long if you run everything electrical in the trailer, at the same time.)

You'll know when one or both of the batteries go bad. When they have been fully charged, immediately after disconnecting from shore power, the voltage and current will be too low to operate anything but lights, and they will be dim. If you measure the voltage, it will probably be 10.5 volts or less.

I'd also check on adding a marine battery (isolation) switch to help batteries last while in storage.

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