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Old 04-03-2015, 06:49 PM   #1
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Long term storage test on batteies

For some time now I have been preaching that there is no need to remove batteries from your Airstream in the winter and keep them on a “trickle charge” or even periodically charge them at all. There is no need to keep them where it is warm to keep them from freezing. All that needs to be done (assuming they are in good condition to begin with) is to fully charge them, clean the tops, and then totally disconnect them, meaning at least the negative terminals are not hooked up to anything at all.

I thought I would run a test this winter to gather figures to support my statements.

I have two group #24 Interstate batteries which came as original equipment on my 2014 FC 20’. I used them for the first season of the summer/fall of 2013 and then in the spring of 2014 I replaced them with a pair of 6 volt golf cart batteries from Costco. I wanted more battery capacity, and that switch out increases the Amp Hour rating from approximately 150 with the pair of group #24 to about 220 with the pair of golf cart type batteries.

The original Interstate batteries had never been abused and the trailer was not a lot demonstrator, so the batteries were never subject to “lot rot”. They did sit around on the basement floor most of last summer, but were fully charged.

Last fall I fully charged them both with a good quality charger. I then put one of them in a chest freezer in the basement for the 5 month time period of November 1 to April 1 of this year. The freezer runs from 0 to +5 F.

So, that battery sat at about 0 F for 5 months. It was not charged or touched in any way, just sat in the freezer.

The second of the pair sat on the concrete floor of my basement for the same 5 month period. I would guess the average temperature was about 35 to 38 F. It also was not touched, or charged.

The starting voltage for both batteries was 12.67 volts last November 1. On April 1 I brought both of them into my warm living room where they came back up to room temp, of about 72 F over 24 hours.

When the voltage was measured, the one which had been in the freezer for 5 months measured 12.59 volts. The one which was simply on the floor of the basement for 5 months measured 12.57 volts. BTW, my meter is a professional quality Fluke digital.

By the chart I have:

100% charge 12.7 volts
95% charge 12.64 volts
90% charge 12.58 volts
85% charge 12.52 volts


So, my two year old Interstate batteries, stored for 5 months at 0 F and 35 to 40 F lost less than 10% of their initial charge. Note that their starting voltage indicated that they were not at quite 100% charge to begin with, but not far from it.

Then I ran a capacity test on the battery which had been held at 0 to 5 F for 5 months. It was NOT re-charged, it was with the same charge it took in late October 2014.

I put a load of 4.86 amps on it for 6 hours (an old auto headlight on high beam) which is 29 amp hours total (6 x 4.86 = 29). I figured that since it was down about 10% to begin with, this would bring it down to about 50% capacity, assuming all was well with the battery. Remember that a group 24 battery has a total capacity of about 70 to 75 amp hours.

After waiting 2 hours to develop the resting voltage which is the only way to measure capacity, I found it to be 12.23 volts. My voltage to % of charge table lists:

55% charge 12.24 volts
50% charge 12.20 volts

So, my load of 29 amp hours on a battery charged last October and stored all winter at 0 to 5 F only brought the battery down to slightly over half charge.

I just went out to measure my Golf Cart type batteries in the FC 20’ which have been sitting outside in the Airstream battery box in north central Idaho all winter, with no charge having been applied since last October. They actually measure 12.77 volts, which is pretty impressive considering they are about 45 F and 100% charge is listed as 12.70 volts!

Repeating myself, there is no need to take batteries out of your Airstream and store them inside and periodically charge them in the winter. Fully charge them to start, disconnect them from any possible load and clean the tops. They will not freeze. They will not lose their charge. They will not suffer damage.

Actually storing them where it is warm is probably harder on them than where it is cold.

I got my first Airstream in 1979. I have had 14 or so of them over the past 36 years. I have never removed batteries. My golf cart type batteries last me 8 to 9 years. I moved to 3 stage chargers when they became available, but prior to that I never allowed the single stage chargers to run 24/7. Even now I do not run my 3 stage chargers in the winter.
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Old 04-03-2015, 08:26 PM   #2
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did you have to modify the battery box for the 6V's?
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Old 04-03-2015, 08:32 PM   #3
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idroba, great test. You did hit on the key...., cold temperatures. Most manufacturers quote a self-discharge rate of about 3% a month at room temperature. Your results, at your temperatures, are spot on with their published graphs. But it sure is nice to see a real world test to confirm this. Good job.
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Old 04-03-2015, 10:58 PM   #4
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Quote:
Originally Posted by Airtandem View Post
did you have to modify the battery box for the 6V's?
Yes, the top needs to be raised. See post #18 on this thread:

http://www.airforums.com/forums/f449...-124829-2.html
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Old 04-04-2015, 08:38 PM   #5
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Great discussion. Thanks. Now, if the batteries are left in place in the Airstream battery box all winter in a northern climate and nothing else is done, so their charge is allowed to drain down, what happens?
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Old 04-04-2015, 09:02 PM   #6
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Great info!
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Old 04-04-2015, 09:39 PM   #7
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Originally Posted by MaineStreamer View Post
Great discussion. Thanks. Now, if the batteries are left in place in the Airstream battery box all winter in a northern climate and nothing else is done, so their charge is allowed to drain down, what happens?
If you fully charge the batteries, then disconnect the them (negative terminal on both) and clean the tops, nothing will happen. They will be fine in the spring.

If you don't fully charge the batteries, disconnect them, and leave them dirty, they will slowly discharge due to some conductance through the dirt on top, and some "phantom loads in the trailer which over several months will pull the batteries down. When they are discharged like that, they will ultimately sulphate and you will never bring them back up to full capacity. If they become fully discharged, they could even freeze and break the cases.

Leaving them in the cold, in the box, with no charging is fine, as my information above shows, BUT... you MUST have them fully charged to start and they MUST be disconnected from any load.
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Old 04-05-2015, 10:00 AM   #8
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Thanks Idroba! Reading your test was like reading a mystery! (I wondered what would happen next!) Great info.

Yesterday I visited the AS in storage. Job #1 was putting the batteries back in - I kept them in the garage the past 6 months, charging with a trickle charger. It took me an hour looking at the wires, studying the picture I took last year, and of course trying to find the washers that I kept dropping to the bottom of the battery tray. And now I know that I didn't even need to take the batteries out for the winter!
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Old 04-05-2015, 11:38 AM   #9
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Quote:
Originally Posted by RAH View Post
Thanks Idroba! Reading your test was like reading a mystery! (I wondered what would happen next!) Great info.

Yesterday I visited the AS in storage. Job #1 was putting the batteries back in - I kept them in the garage the past 6 months, charging with a trickle charger. It took me an hour looking at the wires, studying the picture I took last year, and of course trying to find the washers that I kept dropping to the bottom of the battery tray. And now I know that I didn't even need to take the batteries out for the winter!
Yea! That was my goal, to reduce the pain of owning an Airstream. Dropping washers into the battery box is real fun, eh? Just hauling the batteries around my home to do the test was more than I needed to do. They still have to go back to the basement. But they had to be brought up to about 75 F which is more or less "standard" test condition.

So, you now know the drill: Fully charge the batteries with your built in converter/charger (run it 48 hours or so), clean the battery tops, disconnect the negative terminal at the batteries (both) and wait for spring. Oh, check the water level prior to charging.
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