Solar panel charges battery to 100% then drops

[Chewman]

My 2020 G19FD has a 100 watt solar panel. For the last couple of years I never disconnected the battery with the key and the solar panel kept the batteries charged. I put a cover on the trailer a couple of months ago and since the solar panel was not getting any light I disconnected the battery by using the key. I was plugging into the house current about 1/week to keep the batteries topped off (key back on). I have uncovered the solar panel and now my batteries show a charge of 100% around 2:00 PM and then it will drop down to 80% in a couple of hours. In the morning the batteries are down to about 60% and it takes many hours in the direct sun to bring them up to 100%. 4 months ago it would bring the batteries up to 100% in a matter of a couple of hours. I don't know where to start looking for the problem with the batteries dropping from 100% to 80% when in the direct sun. The batteries are Interstate marine deep cycle and have not been discharged past 50% more than once.
Any suggestions or ideas would be much appreciated!

[eric1514]

Get that battery load tested. It may not be able to hold a charge. You may have taken good care of it but the dealer might not have.

[Flybob]

When you sort this out, I recommend you either keep it plugged in, put a battery maintainer on it, or shut the power off with the disconnect (Key). If you miss a week, the parasitic loads could drain the battery. Repeating this cycle with charging could significantly shorten the life of the battery.

[nvs4602]

When was the last time you put water in your batteries? If you haven't fill each cell with distilled water to the fill line.

[nvs4602]

Also do yourself a favor and put a shunt meter in. The cheap AiLi Battery Monitor on Amazon for $44 is well worth the price to know what's going on with your batteries.

https://a.co/8Kv350Z

You can see the shunt mounted on the wall off of the negative side of the battery.

[clintbonnie73]

The only good way to check acid filled batteries is to use a Hydrometer.. easy check... but make sure you check the batteries after a full charge.. get yourself a:

https://www.napaonline.com/en/p/BK_7...pressionRank=5

[Tom48]

Are you sure your KEY actually, fully disconnects the battery from all loads? I suggest at least a check with a DC clamp meter before ASSUME that it is a complete disconnect.

Also DITTO to pulling the batteries for a load check.. Before I became OBCESSED with battery awareness, we used up two batteries every season in my friends TH that he shared with me.

[savi18]

Just had this with mine, took batteries out and side casings had swelling, had them load tested and no good, so am buying 12v LiFpo batteries as we speak.

[Chewman]

Many thanks to all for the advice. With the key out there is a parasitic drain from something so I would plug in the trailer or expose the solar panel with the key back on. The both would bring it up to 100% but not as quickly as it used to. I will pull the batteries and have them load tested, the batteries were installed March 2020.

[Chuck_S]

Your batteries are unlikely 100% charged certainly not in the tiny amount of time they're being charged.

Their surface voltage will certainly climb to "full charge" 12.7vDC in a "couple hours" but like beauty that charge is only skin deep. Anything less than 24 hours on a good charger is unlikely to bring a discharged battery to 100%. The last 20% of the charge will take as long as the first 80%. Using voltage as a charge indicator only works if the battery has been at rest for 24 hours -- neither charging nor discharging.

Unless you have an amphour meter ("shunt" type meter) that measures flow into and out of the battery you won't know the charge.

-- Chuck

[ScottBrownstein]

If by 100% charged you are referring to the little group of LEDs on the panel, if you look closely the top LED doesn't say 100% it says "charging." It measures the voltage on the bank and all lights are on when it rises above something like 13.4 or so. As others have said, that doesn't mean the batteries are charged, merely charging.

Agree you should get a good shunt SOC meter. They don't cost that much any more.

[Chewman]

Thank you very much for the information! I have a 100 watt solar panel with the Go Power panel on the wall which I am looking at for the charge coming from the panel and the battery level state of charge.

I will pull the batteries and take them down and have them load tested. I contacted Interstate and the 24M-DP only have a 12 month warranty, so I am probably due for new batteries (mine are 28 months old). I have been very careful not to let them run down past 12 volts, but I learned this after I ran them down to the point the TV/DVD player stopped working (4th trip we took). Interstate told me their batteries can be run down to 11.7 and it will respond back to 12.4

I'm sure I'm going to be in for new batteries, now the question is 2 12 volt in a series or 2 6 volts parallel.

Thanks!

[Chuck_S]

Load testing is for starting batteries, not deep cycles. Yours are probably "dual purpose" starting/house batteries but they never start anything so don't bother risking the acid spills to have them load tested. But your batteries on a charger for 24 hours then disconnect them completely for another 24 hours and measure the voltage. It should be at least 12.6v if the batteries are good. Yeah this takes two days.

12.0vDC is just a tad under 50% charged but not enough to matter. But that's just measuring surface voltage the only thing a meter can read.

As for replacement batteries if you have the room for two 6v GC6 batteries I recommend them. I've been using these since 2005 (not the same batteries) and they're powerful and inexpensive. Others will recommend Lithiums but they're obscenely expensive for our use.

Again, and as others have recommended, you need an amphour meter to determine your use and what you have left. Minor learning curve and some settings to make but once dialed in will give you accurate data of how much power you have available.

-- Chuck

[eric1514]

Originally Posted by Chewman

...

I'm sure I'm going to be in for new batteries, now the question is 2 12 volt in a series or 2 6 volts parallel.

Thanks!

You've got that backwards. Be careful.

I would go for 2 6v in series. That's what I did only I bought 4. Costco has them now at $99 each.

[JimM2109S]

Chewman, if you plan to keep the camper long term, buy lithium batteries. "Buy once, cry once". They'll last you forever and can be drawn down to 10% of capacity without long term damage. If you cold weather camp, take the necessary precautions.

Also, wash your solar panel. It is surprising how dirty they can get, reducing efficiency.

[Chewman]

Many thanks to all for the information, greatly appreciated!

[Tom48]

Originally Posted by Chewman

Thank you very much for the information! I have a 100 watt solar panel with the Go Power panel on the wall which I am looking at for the charge coming from the panel and the battery level state of charge.

I will pull the batteries and take them down and have them load tested. I contacted Interstate and the 24M-DP only have a 12 month warranty, so I am probably due for new batteries (mine are 28 months old). I have been very careful not to let them run down past 12 volts, but I learned this after I ran them down to the point the TV/DVD player stopped working (4th trip we took). Interstate told me their batteries can be run down to 11.7 and it will respond back to 12.4

I'm sure I'm going to be in for new batteries, now the question is 2 12 volt in a series or 2 6 volts parallel.

Thanks!

My vote is two new GC2 6 volts. Or spring for lifepo. Amazon shows the Will Prouse approved AmperTime 100 amp for $399. Battleborn told me years ago that the GoPower PWM controller is adequate on the AGM setting

[Tom48]

Originally Posted by Chewman

Thank you very much for the information! I have a 100 watt solar panel with the Go Power panel on the wall which I am looking at for the charge coming from the panel and the battery level state of charge.

I will pull the batteries and take them down and have them load tested. I contacted Interstate and the 24M-DP only have a 12 month warranty, so I am probably due for new batteries (mine are 28 months old). I have been very careful not to let them run down past 12 volts, but I learned this after I ran them down to the point the TV/DVD player stopped working (4th trip we took). Interstate told me their batteries can be run down to 11.7 and it will respond back to 12.4

I'm sure I'm going to be in for new batteries, now the question is 2 12 volt in a series or 2 6 volts parallel.

Thanks!

My vote is two new GC2 6 volts. Or spring for lifepo. Amazon shows the Will Prouse approved AmperTime 100 amp for $399

[Chuck_S]

Lithium batteries are undeniably the best currently available but a pair of GC2 6v batteries are more than good enough and are drop in replacements for the little batteries dealer put on the tongue. Note Lithium batteries require a higher charging voltage than lead-acid types so an ungraded converter is required as well. You don't need a compete power center just the converter that hides inside.

-- Chuck

[Mr Towed]

Going down to 60% in one day in an RV that is sitting idle is a huge drop, in my mind. That sounds like something much bigger than a parasitic drain or a battery issue.