February 19, 2017 § 2 Comments
At first glance, batteries are a terrible investment. It seems that everything you do with a battery shortens it’s life.
When we purchased our trailer, we were not instructed on proper care and use of the lone twelve volt battery that resides in a special vented compartment in the rear of our Casita travel trailer. When the battery didn’t have enough energy left to light the lights, we knew we had to charge the battery. After a while that didn’t work so well and we would get a new battery. If that was within the one year warranty, we received a replacement battery without paying for it. If not, we paid for it. We figured it was just a cost of using our home away from home.
After a few years, it sunk in that there might be a better way. Many RVers use the 50 percent rule meaning that they try to never let the batteries fall below 50 percent of the capacity before recharging. This rule is intended to extend the battery life. We used that for a while but as we learned more about batteries, and studied the life cycle charts, we decided that limiting the battery discharge cycles to 20 percent as a goal extended the probable battery life much more. Especially so for the readily available and cheaper ‘marine’ batteries we are using. So we now aim to limit the discharge to no more than twenty percent of the total capacity leaving eighty percent state of charge. Since our single battery is rated at about 91 amp hours, that limits our use to around 18 amp hours between charges. We enjoy watching television in the evening so we are liable to need to run the generator some in the evening especially in the winter with longer night times and maybe some furnace use. To eliminate the use of the generator in the evening, we added a second battery. It won’t fit in the trailer so it resides in the van and connects to a plug-in that then connects the two batteries in parallel doubling the available amp hours to 182. This allows us to drain around 36 amp hours before needing to recharge. This is plenty for us on a daily basis.
But wait – batteries don’t keep their original capacity. They gradually lose capacity. We are now operating with a capacity estimated to be around seventy amp hours with both batteries. That means we can use something like 14 ah between charges to stay with our twenty percent usage goal. But these batteries are old and slated to be replaced so we’ve temporarily abandoned that goal until we have new batteries. Our new goal for now is fifty percent which is around 35 ah.
Recharging the amp hours we use still has to take place. We do that with our generator or our solar panels if there is sun.
We have two 100 watt solar panels that we move around to wherever the sun is shining. It’s not unusual for the panels to produce over eight amps to the batteries after the controller throttles the power down to a safe level.
The solar controller is located in the trailer above the batteries and was indicating a 16.3 volt current coming to the controller from the solar panels when this picture was taken. The current from the panels is often over twenty volts.
The battery monitor however is showing that the controller has limited the voltage to 14.16 volts to the batteries. We would prefer the voltage limit to the battery to be 14.4 but that is a subject for another essay.
All this has allowed us to live off the grid here in the Sonoran Desert very comfortably for over four months so far this winter and we shouldn’t have to replace our batteries as often. We are hoping the new batteries last at least five years. We’ll see!