Periodic charging and dis-charging of stock battery - why?

[gordo999]

Hi - I have a new Imagine 2400BH and we have now done a number of successful trips over this summer.

I am seeing some strange charging and dis-charging of the battery while the trailer is sitting on my driveway. I have a bluetooth battery sensor connected and see the attached photos where the battery voltage rises to ~12.4V at between 10-11am and then at around 4-5pm it dips down to ~10V overnight.

I have the stock solar panel and the stock 12V Fridge. It's a stock lead battery - see photo of label.

On my driveway I think the only draw on the battery is the fridge, bluetooth battery sensor and a bluetooth TPMS sensor, everything else is switched off. I've tried turning on and off the electrics with the red switch in the basement and the behavior is pretty much the same. (The last two days you see on the time-series photo are when the red switch is OFF, the other four days have the switch ON).

Is this behavior normal? Why is this happening?

Thanks for any help and insight.

[stroguy]

Small current drains not on the disconnect are smoke detectors and CO2 alarm box. There may be another or two that are not disconnected. Some have reported refrigerator 12V needs may not be disconnected either.

[Hoopy Frood]

I'm no expert by any means, but the cycle appears about right to me. Down at night due to fridge and other draws, up during the day due to the solar. My concern would be how low the battery charge gets. I believe that is enough to damage the battery if allowed to continue. But like I said, I'm no expert.

One thing I would do is determine what all is drawing power, both with the Battery Disconnect Switch "ON', and with the Battery Disconnect Switch "OFF".

[sande005]

It is likely mostly the fridge at night. The other draws mentioned are there, but are pretty small, so on their own would take many days to run down a full battery. Batteries can give low/very low readings when under load, that bounces back when the load is taken off. Best test is with no charging/load after letting them "rest" for a number of hours, then see what the voltage is. That load is probably also why the peaks from charging aren't as high as one might like to see. Best to test once just after charging, and again after their greatest use (resting beforehand) to judge whether they are doing well or not.

That said, a group 24 battery is pretty small, and doesn't have a great deal of capacity. Typical dealer item - it's cheaper for them. Consider going to a bigger size battery.
When shopping, look for either the "RC" (Reserve Capacity) rating or the "Amp Hours". Two different ways to measure how long it may last. Not directly interchangeable, so use one or the other to judge. Ignore the "CCA" rating - that is meaningless for this kind of use.

[Rabbit]

Look into how drawing down to 10v affects a standard lead acid battery. From what I’ve read, I believe it damages the battery plates.

[Riverbug]

Each discharge below roughly 50% will begin to cause damage to the battery. Wouldn't expect it to last too many years with that pattern.

[stroguy]

What model fridge? What is the power draw on the 12V for the fridge?

I found this Furrion 10cu ft that draws 11A. Seems like quite a draw. Says it only runs on 10.5 minimum so I would also be concerned of damage to the fridge if the batteries are that low. I would hope the fridge would have a cutoff circuit at that 10.5 level.

[sande005]

A bit of math:
The snip above indicates the fridge uses about 1.08 kwHrs per day. That translates to about 90 amp hours.
The picture shows the battery is rated for 81 amp hours.
So at those rates, will last about 21 hours. For max life, only about 40 AH should be used most of the time. Going somewhat more won't kill it immediately, but it won't last as many years as it could. Depends on consistently how much "somewhat more" over time.
Let's just call it 12 hrs per day without recharging as conservative "good" use.

All of this is rough numbers - fridge temps, air temps, will all have lots of bearing on how long the fridge actually needs to run, and could wildly change the daily energy usage.
Using other things will have a big impact too - lights, the parasitic draws mentioned, water pump, furnace fans, jacks, slides, etc.

The good news is that from the results shown, the overnight drop is not getting worse each day - meaning the solar seems to be replenishing what is being used overnight. Tracking longer would give better confirmation of this. I'd guess that one is seeing the artifact of the battery being under load. No load testing would verify if it is really dropping that low.
The bad is that there is unknown margin for operating other things.
A basic test would be to operate a few big draw things around dawn - do the slides move in and out with normal speed? Does the front jack operate at normal speed? Slowness would mean the battery is near fully depleted. Normal is good, but still leaves open the question of "how much more can I push it before it is really dead?"

One might also run a cord to a house outlet, and let the converter give the battery a good, long charge (24 hrs). Then repeat the readings over the next few days. Does it still drop to 10 the first and subsequent nights? Or does it start higher, and drop over following days?