Put the Solar to the test.

I have similar system 300W solar w/ 300 AH of AGM batteries. I run the furnace at 60-64 degrees (my furnace draws less than 4 amps when running). All LED, and all electronics are modern and efficient. No battery usage for heating water, cooking etc-all propane for that.

Usually 12.5 ish when I get up (and nothing's on). Usually up to the 14.4 volt regulation point by 11 or 12 AM.

A few days of cloudy cold weather could throw this for a loop-with the furnace running 24 hrs and little recharge-but there is the generator. In general my off grid trips are a week or less and if there is a deficit, the solar can handle it later.

scrubjaysnest wrote:
This chart is only ball park and isn't correct for many batteries.
For my Exides 90% is 12.7 for an example and 50% is 12.4 volts.
Best to check the manufactures website for your specific battery.

Resting or under load?

The chart is for about 5 to 25 amp load like when the furnace is running.

Nothing wrong with voltage dropping into the elevens periodically while under load. The battery is supposed to work for you, not you working for the battery. Your system seems to working very well for you and will serve well for a long time.

Well, I have to say it didn't realize that 11v was "dangerously" low. I also didn't realize that 12v systems dropped such high percentage points for such low decimel drop. Most mornings it was around 11.9-12v. Just the one morning that we had a visitor that has a bad back so we kept the trailer at 65 degrees. I don't see me going to a different type of heat. I am aware and have been for many years that the forced air type heat in an RV is super parasitic on the batteries but there is not room in this rig for a catalytic type heater and it's not my thought that we will be in weather colder that 20 degrees, at least not for any length of time. I will likely install two more 6v batteries to keep things happy. I just love posting a thread like this and getting all this great information!

Vintage465 wrote:
run the forced air furnace to keep the trailer @ 60 degrees each night for a week and the lowest voltage I woke up to was 11v(kept it at 65deg. that night).

Try 55 and see if that helps. You don't want to be dragging them down to 11 very often.

Well, when you KNOW your batteries are not getting to 100% each day, you sure don't need to check SG. I have no use for one myself.
After a couple weeks when battery performance is lacking because of the 80% charges, I mite use the little genset for a couple hrs one day, then let the solar take them to 90-100%, and I'm good to go for another couple weeks. I don't care much about 100% all the time. And when I get back home and on the grid, the PD makes them like new again.
My 12'ers are near 6 yrs old, doing great,........and w/o a hydrometer !

Don't want to highjack your thread but just throwing more into the conversation for comparisons.

I disconnected 2 panels this morning so I'll try using 260 watts to replace 78 ah into 4 six volts (Sams club/east penn). Solar is doing 5.8 A right now @ 7:00 am and 4.4 A is going into the batteries. South west desert.

I have been running my 255AH battery bank since 2009 and we typically run about 20AMPS DC Current from the batteries each evening between 6PM and 11PM and of course have the 1-2AMPS parasitic drain all the time when camping off the power grid.

My 255AH battery bank makes it just fine through the night and drops my batteries to around their 12.0VDC charge state around 8AM each morning.

This is when I use my 2KW generator when allowed to re-charge my battery back up to their 90% charge state by connecting the trailer shore power cable directly to the generator.


I am just now thinking solar panels and will have around 400WATTS installed on my POPUP trailer roof. I want to get a good 20AMPS of usable DC current from my panels during the high sun day.

I am pretty sure I will have to get past my initial high DC current charge demand of around 52AMPS DC current using my 2KW Generator for around an one hour run until the battery bank starts tapering back to its 8AMPS or so DC current demand from the charge source. Then I can shut down my 2KW generator and let the solar panels continue the charge for rest of the high sun day.

I have learned over the years since 2009 I can not start my battery run if I have less than a 90% charge state otherwise it will get dark on me around 10PM at night.

The 2KW Generator will be my priority use item and the solar panels will be a supplement use item in my case.

It is a bit different camping off-road here on the East side of the US and everywhere you go you run into generator run time restrictions. I also suspect Solar panels will not get as much high sun as you find out west.

We all have our different needs for things it seems...

Roy Ken

11.0V is very low, may be OK if furnace was running at the time as loads lower the voltage and don't reflect the SOC. A hydrometer would reflect the actual SOC.

A battery monitor would be useful but $150+ or perhaps you could install 2 more batteries?

But your solar/batteries are doing great.

I'm similar use but 520 watts with a 40 in led television. I have 2 strings of six volts. I have run on one string and touched 11.7 volts overnight. I like to stay above 12.1 or 12.2 so it takes four six volts for that. The key thing that is good for you is that 300 watts of solar is replacing what you used. If you go to 4 batteries you will stop going so low on the battery.

I do read over and over that best battery life is when kept above 12 volts to 12.2. If you have wet cells check the specific gravity from time to time to be sure your system is fully charging you batteries. They may appear to charge 100% but will get lazy as the sp drops. My solar controller is set to return 115% of my daily amp hour use. It makes up for system inefficiency and battery internal resistance. Your controller may have similar capabilities.