Ques about my batts

After 4 months into our fulltiming with most of that being dry camping/boondocking relying solely on our solar set up, I've got a question for you all...

First, what we have:

two 158w panels into a 30A mppt charge controller charging up three group 29 deep cycles with (per the suggestions of most on this forum) all manner of switches, fuses, correct gauged cables, 1300 pure sine wave inverter, etc etc etc...we had intended to go basic with this and over the course of this last summer, during our renovations, slowly upgraded every link in the chain (one upgrade would require another and another and another) This set up has done us well, and we have yet to run out of power.

Even on cloudier days the external digital meter reads 100% batts by noon/1pm...when we drive we are charging, when we are plugged in we are charging and of course, the sun is charging...while these are happening the meter reads 100% pretty consistantly, however the min the sun goes down (without anything on) the meter will tick down and hover around 58-49% we will then use lights, charge our laptops/cell phones, watch a little tv at dinner time and by bed time the meter reads upper 20s.

To be honest; the one puzzle piece we skimped on financially was the meter....it's a pretty junky/basic Japanese meter off ebay....at the time we had already sunk 3X as much as we intended to into the system and felt a cheap one was better than not having one. So my suspicions are that this meter is junk and doesn't know what it is talking about.

But the meter showing 20s/30%s everynight at bed time has me worried that we are rendering these brand new deep cycles useless in a year or so...is it normal to see such a drop the min a charge is not going in? Does it sound like I might have a drain somewhere? Could this meter just be garbage and not telling me accurate info at all?

I want to be good to this system I sunk so much money into, any thoughts would be appreciated!

I suspect the meter is telling the truth and it's the charging that's fooling you.  Anytime the converter or the alternator is charging the batteries, that meter will read 100%.  It doesn't mean the batteries are actually at that level yet, just that the charging voltage is there.  If the batteries are slowly getting lower and lower, as I suspect they are, they will indicate that as soon as you start drawing a heavy load from them.

You nee3d to check the water level in them, and then charge them for many many hours to get them back up to full charge.  You may have already damaged them to some degree.

I agree with Lou - the meter is probably showing you battery voltage, which is a fairly crude measure of state-of-charge and meaningless as long as any charger is active (it is measuring the charger, not the batteries). The 49-58% you see when the charging stops represents the actual state of the batteries.

It may be that you aren't getting a long enough charge to bring the batteries up to 100% - it takes many, many hours to do that. It may take 10+ hours after reaching the 80% level to get that last 20% in because the rate of additional charging slows dramatically as the percent of charge increases. A big charger helps move quickly from, say, 30% to 60%, but after that it depends on the ability of the batteries to accept further charging and not the size of the charging source. It's the nature of battery physics and not any fault of your equipment.

However, there is also the possibility that one or more batteries has a high resistance to charging. Lack of water in one or more cells is one common cause. Corrosion on a battery terminal is another.

When you have the opportunity, stay on shore power for 48 hours and then disconnect to check battery charge level. If its stays up around 90-100% for an hour or two (with a light load), the batteries are probably OK. If it drops quickly to under 80%, I would be suspicious of the batteries or connections. a Load Test one ach battery would be my next step, as would a thorough cleaning of every terminal.

We are living off our solar system while boondocking on BLM land north of Yuma, AZ. We have three 135 watt panels. We monitor our battery with a Trimetric 2020 which measures the amps in and out of the battery. We have one or two TVs going during the day and the laptops charging. I also monitor the battery voltage. The battery voltage will always read lower than true due to the load on the batteries. We also have three Group 29 RV/Marine batteries. We have 89 watts more charging power than you. I am in the process of adding a 100 watt panel. This is to add to day time capacity and still get the batteries charged by noon. I am also installing a Turbocool swamp cooler to allow cooling with solar power.

We make it through the day and still have 70% of battery at midnight. I will be changing to Trojan SCS 225 true deep cycle batteries next year. I hope to modify the battery tray to allow four of them, which are Group 31 batteries. I will then have 520 amp/hr of battery capacity.

While charging capacity is a function of your boondocking life style and energy consumption I see many many boondockers in the desert of AZ and 4-6 larger panels is the typical installation to provide enough charging capacity for stand alone panels. If you have a generator you may find it necessary to run it a couple of hours a day to supplement your two panels and keep the batteries fully charged until you add to your panel capacity.


The reason we have no panels is that the 2-3 weeks of boondocking we do annually couldn't recoup the cost of a good system vs burning fuel to run a generator.

Try charging one battery at a time and see if it gets higher for each battery.

I tend to agree that you are not charging long enough.

TheBearAK said:

Try charging one battery at a time and see if it gets higher for each battery.

I tend to agree that you are not charging long enough.

Click to expand...

I found better to charge the battery bank as one.  Assuming all batteries in good condition, equal charging is key.

Couple of side notes here. I don't know if your a 5th or MH, but if it is a 5er, charging through a Bargman plug is "ehhm" not doing much of anything. By the time you push power through 75+ feet of #12 or hopefully 10 wire, not a lot of power. I calculated and measured once that the return (ground) wire had up to 35 amps on it depending on lights, brakes, battery etc. And that will really drop the battery charge availability.

Motorhomes are not much better, same size wire but shorter lengths, but a lot less ground loads.

Remember that you have 2x length for the wire - out and back, and with 12 volts any loss is significant.

We have a 5'er and I invert to 120 volt in the truck and feed 120 volt into the charger in the trailer. (4 amps at 120volts = 40 amps at 12 and the charger is 4 foot from the batteries)