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Old 11-06-2012, 08:18 AM   #1
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when to buy batteries?

I left the closet door open this fall and discharged my batteries too far. Couple of years old or so. The will not recharge at all, at least with the univolt.
If I just take both batteries out and tape up the positive leads will the 12 volt system work when plugged into 110 without damaging the univolt?
The trailer is going to sit from Jan - April.
Not sure I am going to use the trailer between now and April. If I do I will have to buy batteries and then probably take them out and let them sit in the garage during the Jan-April period.
Have never really wanted AGM batteries. But have a question. Do the AGM batteries last better in situations where the battery is not used for months or do they deterioate about like flooded cell batteries in that situation.
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Old 11-06-2012, 08:43 AM   #2
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Originally Posted by Bill M. View Post
I left the closet door open this fall and discharged my batteries too far. Couple of years old or so. The will not recharge at all, at least with the univolt.
If I just take both batteries out and tape up the positive leads will the 12 volt system work when plugged into 110 without damaging the univolt?
The trailer is going to sit from Jan - April.
Not sure I am going to use the trailer between now and April. If I do I will have to buy batteries and then probably take them out and let them sit in the garage during the Jan-April period.
Have never really wanted AGM batteries. But have a question. Do the AGM batteries last better in situations where the battery is not used for months or do they deterioate about like flooded cell batteries in that situation.
AGM batteries have a much longer shelf life when in a non-use state due to their much lower internal resistance. I have had Lifeline AGM batteries show no loss of voltage from the time they were shipped to me (12.9 VDC on delivery) to the time of sale 3 months later (still 12.9VDC).

Liquid lead acid batteries will generally their internal voltage to about 12.2VDC (or 50% depth of discharge) from a fully charged state in about a month when on the shelf. But as always, YMMV.
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Old 11-06-2012, 10:55 AM   #3
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If you have a single stage charger, I wouldn't buy AGM batteries unless you intend to be VERY careful about not overcharging them. They're just too expensive. (Actually, any battery is too expensive to be killed this way, but AGMs are more expensive than liquid lead acid batteries.)
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Old 11-06-2012, 10:58 AM   #4
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"Liquid lead acid batteries will generally their internal voltage to about 12.2VDC (or 50% depth of discharge) from a fully charged state in about a month when on the shelf. But as always, YMMV. "

My milage does vary... a lot.... LOL. My experience over many many years and RV's is that a fully charged normal lead acid battery will not self discharge significantly over a period of 6 months of more. If they went to half charge in a month, what would the be like in 6 months? I am a "snowbird" and leave my trailers and my TV with disconnected but fully charged batteries all winter. When I come back in the spring, the TV starts right up after connecting the battery. If it discharged to 50% in one month, as suggested, what would it be like in 5 or 6 months?

I have an ammeter on one of my RV's and when I re-connect the battery after being gone all winter, and turn on the PD converter/charger, the 45 amp automatic 3 stage charger does not charge at more than 3 amps, and then for only a couple of hours. This is using two 6 volt golf cart batteries in series as the house batteries. So, they do not self discharge at anywhere near the rate mentioned in the quote above.

Now, as built at the factory, and charged there for shipment, and never used, a new lead acid battery may drop in voltage faster than one which has been in service for a while. But my long experience is that a fully charged, clean top, disconnected lead acid battery has very little discharge over a 6 month period.

So, yep, my milage does vary. A lot.
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Old 11-06-2012, 10:58 AM   #5
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Newer Airstreams have electronic items that drain the batteries, even when in storage (e.g., the propane leak detector). However, I am unsure whether this is a problem in older models. If you do have "parasitic drains", the only way to keep the batteries from going dead is to completely disconnect them by removing the positive battery cables or using a battery isolator switch.

For details on battery isolator switches, SEARCH for "Perko 8501DP" on this site.

Note: Marketing literature says that in storage, AGM batteries retain a charge better than wet cell batteries, but that assumes there is no load applied. Any battery will eventually go dead with a load present. (Ever left your dome light on in your car while you were on vacation for a week or two?)
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Old 11-06-2012, 11:30 AM   #6
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Phoenix is correct. Note that even when you switch off the batteries using the cutoff switch (under the sofa in the 31 Classic) the lp detector still will be on. Wish Airstream would do like other RV manufacturers and have the battery disconnect actually perform as a true disconnect.
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Old 11-06-2012, 11:51 AM   #7
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Quote:
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Phoenix is correct. Note that even when you switch off the batteries using the cutoff switch (under the sofa in the 31 Classic) the lp detector still will be on. Wish Airstream would do like other RV manufacturers and have the battery disconnect actually perform as a true disconnect.
I moved the power supply for my propane detector behind the battery disconnect, so it is no longer a parasitic drag.
Bill M.,
1. My Battery Minder brought my batteries back from the dead this Spring. EVery Airstreamer should own one.
2. Get rid of the Univolt. Replace it with an Iota DLS-55, and you will be glad you did.
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Old 11-07-2012, 12:35 PM   #8
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Have never really wanted AGM batteries. But have a question. Do the AGM batteries last better in situations where the battery is not used for months or do they deterioate about like flooded cell batteries in that situation.
The thing to bear in mind is that you can wreck AGM batteries just as easily as you can wreck flooded batteries, although the details differ on what particular form of neglect of misuse will wreck them. So, as with tires, you may not get the useful life you hoped for.

As Lewster has pointed out, flooded cells have higher self-discharge rates. Even with the battery completely disconnected and no parasitic load you can lose the charge in a new flooded battery over six months or so, and with years of use they discharge more quickly. Not so AGMs. Flooded batteries also require periodic addition of distilled water, and if you don't water them, they die.

AGMs will discharge and sulfate just like flooded cells though if there is a small load applied.

You can damage an AGM more easily than a flooded battery through overcharging, because there's no way to add water.
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Old 11-07-2012, 01:24 PM   #9
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Here is a link to the Trojan Battery page on battery storage.

http://www.trojanbattery.com/pdf/WP_...orage_0512.pdf

If you look at figure 1, you will see that the lower the storage temperature, the less the self discharge. At 42F in 19 weeks (almost 5 months) the battery will lose 20% of it's charge. That is what I see when I store my batteries (in the trailer) all winter long, up in the northern parts of the country. My average winter temp. is about 30F so my losses are even less than the lowest temp line shows. For those of you who store their rigs in warmer climates, the discharge rate is higher. You will also see the freezing temps for batteries at various states of charge in Table 1, same page. They are very low, unless the battery is discharged, so freezing is not really a problem. Storing an already discharged battery is death on it, so it will fail either by plate sulfating or freezing or both.

So, those who bring their batteries inside to a "nice warm place" actually have higher discharge rates and will need to maintain them more than if they are left where is is cold.

Again, to store a battery for several months, keep it as cool as possible and be sure it is charged to begin with. Disconnect the battery so there is no possible load on it. Clean the top to prevent discharge through the dirt on the top. If you can charge it now and then, fine.
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