How long to leave AGM battery powered rig unplugged?

[jondrew55]

I know I can add a real disconnect switch or manually pull the the battery wires. That's not what this question is about.

On my 2021 25' GT my flooded cell batteries would start getting very low on charge after about a week (right at 12 V) with the onboard battery disconnect switch turned off. My new 30' GT with AGMs seems to be fairing a bit better than that. So far, I've dropped from 12.9V when I put it in storage to 12.7V. I'd like to feel comfortable leaving it for 2-3 weeks unplugged. Maybe it will stay above 12 V for that long? I do have 15 amp power at storage and up to this point always left it plugged in. But I've had a couple of occasions where I come to check on the trailer or pick something up and the GFI has tripped and I don't know how long it's been without power with the shore power switch on. I do have solar, but it's covered storage so that won't help much.

The previous owner of the 30' kept it plugged in all the time so I assume the batteries are in good condition. Not sure the owner of the 25' was as observant of battery maintenance since he seemed shocked when I asked him what tire pressure he kept it at and he said "I don't know, I've never checked it".

[Silvr_Bullet]

A proper functioning AGM in cooler weather with no load will be fine for at least a month, warmer weather less.

addendum, with the carbon monoxide detector drawing current, I wouldn’t trust it more than a week.

[hoppes-no9]

Originally Posted by Silvr_Bullet

A proper functioning AGM in cooler weather with no load will be fine for at least a month, warmer weather less.

addendum, with the carbon monoxide detector drawing current, I wouldn’t trust it more than a week.

That’s my conclusion based on my recent experience, especially the addendum

[uncle_bob]

Hi

Like it or not, voltage is not a great way to determine battery state of charge. Your "starting point" could be at 80% or at 100% and you still would have roughly 12.6V on your monitor. Since you stop at 50%, this is a pretty big deal.

Next up, capacity changes with temperature. If it's freezing out, you aren't going to get as many days as if it's 120 degrees in the shade. Temp also impacts the magic battery voltage readings so you may decide the battery is dead when it's still well above 50% ( if it's hot out ....).

Flooded cells ( at least the stock ones ) aren't quite as high quality as the (stock) AGM's. They also need to be checked regularly for fluid level and "topped up". In Florida it is an issue. In Arizona it's a very big issue. If you are used to camping in Nova Scotia and find yourself in Tucson all summer, your battery habits may need to be improved a bit .

All batteries can be damaged. You never quite know how this or that set got treated as part of the delivery process. If the trailer is used, who knows what the PO did or didn't do. The stock AGM's are a bit more tolerant of abuse than the stock flooded, but neither is likely to be happy with a lot of abuse.

One of the (as yet) unmentioned parasitic drains is the inverter (if you have one). Reports area all over the map for power off inverter current drain. Some folks seem to have ones that are really crazy. If yours (like theirs) pulls a quarter amp (yikes !!!) when shut off, that's 6 AH a day. Good luck with your two week plan on that rig. Yes, I'd claim that's a defective inverter ..... who knows ....

Bottom line: If it's parked, plug it in.

Bob

[jondrew55]

Originally Posted by uncle_bob

Hi

Like it or not, voltage is not a great way to determine battery state of charge. Your "starting point" could be at 80% or at 100% and you still would have roughly 12.6V on your monitor. Since you stop at 50%, this is a pretty big deal.

....

Bottom line: If it's parked, plug it in.

Bob

Except my power is unreliable at the storage facility and I assume the draw his higher if the shore power switch is in the "operate" mode and will kill the battery faster. I suppose I'll have to bite the bullet and put in a real disconnect switch. Pulling the terminals off is a bit of a pain the way they have these things wired up.

[richard5933]

Originally Posted by jondrew55

Except my power is unreliable at the storage facility and I assume the draw his higher if the shore power switch is in the "operate" mode and will kill the battery faster. I suppose I'll have to bite the bullet and put in a real disconnect switch. Pulling the terminals off is a bit of a pain the way they have these things wired up.

A real disconnect switch is the answer.

And, if you have a shunt battery monitor like the Victron 712, consider putting the disconnect on the negative side of the battery bank. Depending on how they are connected the shunt systems can still pull a small drain on the batteries even with the disconnect on the positive. Mine does it through the combo temp probe/power supply to the shunt which is on the positive side of the battery bank.

[uncle_bob]

Hi

Parked = sitting at a campsite with folks here and there

Storage = something different than parked

Bob

[jondrew55]

After charging my batteries for 2 says, they seem to top off at 12.9 volts. The trailer sat with the shore power switch off for 10 days and it dropped to 12.7. As uncle Bob pointed out, voltage is not a perfect indicator of state of charge, but for my purposes it looks like I can safely leave it off for 2 weeks with no worries.

[WellSaid11]

Although you said your question is not about a disconnect switch, what Richard said at Post #6 is correct.

Wire yourself a disconnect switch to your negative.

Done.

[Glenritas]

Co and smoke detector is on all the time and pulling power regardless of the disconnect switch position.
You will have to disconnect it for long term storage. Reconnect when getting ready to take out of storage .
How you do this is up to you .

But Do Not occupy the trailer without it connected.

[WellSaid11]

and don’t drive it while the full disconnect has been switched.

[jondrew55]

I know what the right answer is. But I’m lazy and have other things going on. Not to mention I’ll bet most people have no idea what this issue is and run their batteries into the ground without even knowing it. I wonder if having the shore power switch on creates more draw than thos parasitic loads from the CO detector assuming you have everything else turned off? If that’s the case, I’d be fine just leaving it plugged in at storage and not worrying about the power going out from a GFI glitch?

Originally Posted by WellSaid11

Although you said your question is not about a disconnect switch, what Richard said at Post #6 is correct.

Wire yourself a disconnect switch to your negative.

Done.

Attachment 418315

[uncle_bob]

Originally Posted by jondrew55

After charging my batteries for 2 says, they seem to top off at 12.9 volts. The trailer sat with the shore power switch off for 10 days and it dropped to 12.7. As uncle Bob pointed out, voltage is not a perfect indicator of state of charge, but for my purposes it looks like I can safely leave it off for 2 weeks with no worries.

Hi

With the charger connected, a full charge should be up around 13.2 to 13.4 volts. That's measured at the battery terminals *with* a good multimeter. Once you disconnect the charger for an hour or two, they should settle to 12.6 or there about.

All battery "magic voltages" are temperature dependent. They vary by a half volt or more over a fairly normal camping temperature range. The numbers above are for a 70F sort of battery temperature.

If you are looking at the stock battery readout, who knows what you will see. They can easily be off by a a few tenths even with no load. Toss in load and you get another couple tenths.

Bob

[jondrew55]

Sure, 13.2 and up is typically what I get when connected, although sometimes it seems lower when the batteries are topped off.

Originally Posted by uncle_bob

Hi

With the charger connected, a full charge should be up around 13.2 to 13.4 volts. That's measured at the battery terminals *with* a good multimeter. Once you disconnect the charger for an hour or two, they should settle to 12.6 or there about.

All battery "magic voltages" are temperature dependent. They vary by a half volt or more over a fairly normal camping temperature range. The numbers above are for a 70F sort of battery temperature.

If you are looking at the stock battery readout, who knows what you will see. They can easily be off by a a few tenths even with no load. Toss in load and you get another couple tenths.

Bob

[majorairhead]

My unit is stock, with the lifeline AGM's. When I plug in my 50 amp at home the charge will settle in at 13.6v. (In the garage, no solar)

Somewhere around two days later it'll drop to 13.2, some times 13.1.

I'll unplug the 50 amp cord and shut off the "use/store", er "battery disconnect" switch.

The voltage of the batteries the next day will read 12.9, and will slowly fall over two weeks or so to 12.6/12.5, depending on how much time we spend doing little things in the trailer.