Winter storage: batteries

[obgraham]

OK having failed to get an answer in three other places, let's try here:

What do you all think is the best way to store a B for 2 unattended months? In this case I'm talking Roadtrek CS, E-Trek variety, so it has 8 AGM's. Storage is indoors, so the solar charger will not keep things topped off. The chassis batteries can be disconnected, via the plug under the dash. OK.

But due to a peculiarity of the ETrek, the house batteries do NOT charge when on shore power, unless the inverter is running (it really is a "charger/inverter", no separation of function). So here's the choices:
1.Shore power ON, Inverter/charger ON. It will then run full time, including its fan, for the two months. Unattended I'm not sure that's so safe.
2.Move it outside to allow solar to keep things up. Yecch. Why did I build a big shed?
3.Charge everything, then shut her all down and leave, hoping those AGM's will hold some charge. This is the simplest.
4.Do like #3, but disconnect the negative cables on the AGM's before leaving.

Any wisdom here? (None from RT so far!)

[markopolo]

I have solar panels on my van also but store the van in a garage.

When it comes to lead acid batteries (AGM, wet cell) I subscribe to the "a fully charged battery is a happy battery theory". My van is plugged in all the time it is in the garage. Four batteries, 2 house & 2 chassis, are kept at float voltage. I might not use it for 4 consecutive months in winter but keep it plugged in. The 3-stage converter/charger has a fan but it very rarely turns on.

That's what I'd do if I had your rig unless specifically advised by either Roadtrek or the inverter/charger manufacturer to do otherwise. I'd contact the inverter/charger manufacturer if the topic of continuous operation is not covered in the inverter/charger operation manual.

These rigs are getting a bit complicated to be disconnecting batteries for storage without knowing what affect that will have on other components. For example, there might be some small output from the solar panel while the van is in the shed. Will no batteries connected affect the solar controller in any way?

Two months is not that long for storage as long as everything is really off, with no parasitic or phantom loads. If you choose that route I'd make sure the batteries are fully charged by plugging the van in for a day or even two days before turning everything off for storage.

[gerrym51]

Originally Posted by obgraham

OK having failed to get an answer in three other places, let's try here:

What do you all think is the best way to store a B for 2 unattended months? In this case I'm talking Roadtrek CS, E-Trek variety, so it has 8 AGM's. Storage is indoors, so the solar charger will not keep things topped off. The chassis batteries can be disconnected, via the plug under the dash. OK.

But due to a peculiarity of the ETrek, the house batteries do NOT charge when on shore power, unless the inverter is running (it really is a "charger/inverter", no separation of function). So here's the choices:
1.Shore power ON, Inverter/charger ON. It will then run full time, including its fan, for the two months. Unattended I'm not sure that's so safe.
2.Move it outside to allow solar to keep things up. Yecch. Why did I build a big shed?
3.Charge everything, then shut her all down and leave, hoping those AGM's will hold some charge. This is the simplest.
4.Do like #3, but disconnect the negative cables on the AGM's before leaving.

Any wisdom here? (None from RT so far!)

the solar panels Roadtrek uses just need indirect daylight- how about a couple of skylights in the shed-you did not mention the shed part in your other postings

on the other hand marko is right-if the battery disconnect is off and the batteries were fully charged when it was put into storage-a couple of months probably i snot a problem-i'd be more worried about the chassis battery. since your storage shed is close to you why not just run the van for an hour or so every 2 weeks or so.

[booster]

A lot of the inverter/chargers have a method of shutting off the inverter section if you are not using it. Sometimes it is not readily available and may need to be found or a switch added. Especially in storage, there is not any good reason to need the 120 volt power from the inverter, unless the Etrek is using it for some kind of control function. On "normal" systems, the outlets are changed over to directly off shore power, so the inverter wouldn't do anything anyway. Etrek may be different.

We do like Marko, plugged in and in float (with automatic periodic boost) all winter, inside, solar turned off.

A big question would be if it is possible to turn off all the loads in an Etrek. If you can, and it has AGM batteries so they self drain little, you could easily get by leaving everything off, no shore power, except for a quick charge on shore power every 2-3 months.

[Arlo]

Last winter I left my E-Trek in my heated garage (45-50F) for about a month with battery disconnect switch engaged (battery power off, no shore power). House and chassis batteries were fine. Starting with fully charged batteries I'd be comfortable doing this for two months.

[obgraham]

Thanks, Arlo. Real world experience.

I guess there weren't many E-Treks around last winter. After this winter we should see some more experience. I'm leaning to doing just what you did and hope for the best.

In the Spring perhaps I'll resurrect this and see what has worked or not for people.

[Arlo]

Hmmmm. Does anyone know if the rate of self discharge from a disconnected battery bank is linear in time? Seems like it should be. If there's a 0.1 volt drop per week then there would be about a 0.8 volt drop over eight weeks?

Edit: From what I can find on the interweb, AGMs can be expected to self discharge about 2% per month at a constant temperature of 60F (http://www.cdtechno.com/pdf/ref/41_7272_0112.pdf). Linearity in time, after the surface charge has dissipated, seems to be true assuming constant temperature.

[gerrym51]

Originally Posted by Arlo

Hmmmm. Does anyone know if the rate of self discharge from a disconnected battery bank is linear in time? Seems like it should be. If there's a 0.1 volt drop per week then there would be about a 0.8 volt drop over eight weeks?

Edit: From what I can find on the interweb, AGMs can be expected to self discharge about 2% per month at a constant temperature of 60F (http://www.cdtechno.com/pdf/ref/41_7272_0112.pdf). Linearity in time, after the surface charge has dissipated, seems to be true assuming constant temperature.

i am not an expert on AGM batteries but everything i've read seems to indicate a slow discharge assuming there are no loads on them.

[mlts22]

What about leaving the rig unplugged and batteries disconnected... but putting a device like a Battery Minder (they have models specific to AGM banks available) on the batteries? This would offset self discharge. Since the smaller model takes up less than an amp, you would be drawing less than 120 watts at any time.

[Davydd]

Doesn't Roadtrek cover any of this in an owner's manual for winterizing?

[obgraham]

Originally Posted by Davydd

Doesn't Roadtrek cover any of this in an owner's manual for winterizing?

Nope.