Solar Battery Maintainer


Active member
I mentioned elsewhere that I had some engine cut outs, and eventually determined that the Shorai lithium battery I had installed was compromised, discharging over several hours from 13.7 Volts to 10.7 Volts.

How, or why, I don’t really know for sure but probably it had been allowed to discharge too low too often. Cell imbalance, whatever. When I sent the Roreri to TCS that battery had sat in the passenger seat over winter for example—not my fault I expected to get it back by August or September whole other story there. Lithium batteries are light as hell (less than 5lbs for a 540 cca battery) but fragile and really need to be on a battery tender especially in the winter.

I had been starting the motor with a jump pack and once started, it would run but it would still occasionally cut out especially in the morning run to my son’s school—insufficiency of current to run all systems. Or whatever. But the idea was that if I could induce a float charge then it could work.

I had some 20Watt solar cells on hand from a remote site solar array system I had set up, and a charge controller that would cut in current at 13V and cut it out at 14.2V. These are for charging and maintaining RV batteries so I figured why not. I placed a panel on the rear boot fold down deck (a pretty good fit actually and sits nice!) then ran wire to the charge controller and battery then hooked clamps to the terminals.

The test was this morning. The way the trees are here, I only had about 45 minutes of direct but low angle sunlight to go from 10.77 Volts to enough to start the motor. At the moment of truth the battery read 11.63 Volts at the terminals—pretty low. But turn over it did, and moreover, no cut out while taking my son to school which was pretty much an every day happening. After 25 minutes of idling and driving the battery read 13.65 V, and then continued to sit in the sun continuing to charge.

At 12:30 I checked the battery and it read 14.2 Volts at the terminals under full sun. It started right up and I drove a half hour to an appointment. Confident power. I suspect battery insufficiency was causing some microstutters. When I got to my destination, I read 12.99 Volts and rising under charge from the panel, then when I came out an hour later I read 14.22 Volts at the terminals. So, it works.

Is this a real solution? No. I mean, I should not be leaving this ride out in the Colorado sun. But it was a interesting project and workaround. I have a Braille AGM battery on the way. But I might leave that system installed to insure that new AGM battery stays tip top. Or even put the Braille on the floor behind the passenger seat and go two battery.


  • image0.jpeg
    193.6 KB · Views: 5
  • image1.jpeg
    254.5 KB · Views: 5
Last edited:


Active member
Very nice :)

I have an little solar panel at home feeding an normal lead 12 volt battery. This together with an solar regulator.
Works excellent.
It is an stand alone setup just to keep the battery charged from my (emergency) generator.
Believe it or not, it still has the original battery and is in the unit for about 15 years now. Now and then I start the generator to test and always she starts, amazing.