Forum Discussion

Almot's avatar
Almot
Explorer III
Nov 18, 2015

Size of solar maintainer for car battery?

Had a 2.4W panel for $30 or so, on my truck while in storage. Seemed to be adequate at latitude 27 with plenty of sun and almost no clouds. Flat on the roof. Didn't worry much because the battery was dying.

Now getting a new battery. As much as I hate spending $45 on slightly bigger 5W gizmo from Amazon, I'm willing to do this for $100 battery. These small chargers are all overpriced, but it comes with all the cables, cig lighter plug and night diode. Not just a bare panel.

Wouldn't want the panel to boil it at 17V on a nice and warm 105 degree day when I'm not there to take care of it.

Q: What self-discharge current has a truck battery with 600-800 CCA? Or how many AH it can be compared (I know there is no such thing)?

13 Replies

  • I suspect that your current panel may be marginal but as noted it depends on your parasitic loads. You can monitor your battery volatge in the morning before charging starts for a week or so to determine if it is staying at 12.6 to 12.7 or decreasing.

    You can also measure your parasitic load and do the calculation of how many AH you will need to maintain your battery.

    I have maintained a single RV 12V battery in the past here in TX with a 10W panel with some parasitic loads eliminated by pulling a fuse. I think if you go above 5W you should have a controller to prevent overcharging.

    Dick
  • New battery should need less power. Stick with 2.4 if that is working.
  • Not sure I'd bother to upgrade from a 2.4W panel to a measly 5W panel. According to my calculations, the 5W panel would trickle charge your 12.8V battery at ~ 400mA. By my estimate/guess that is about 0.4% of that new battery's AH capacity. The 2.4W panel probably charges at about < 200mA . Neither one of them are in any danger of overcharging your battery, and quite frankly I am dubious they could keep up with just a maintenance charge given they only work during the day, and your 'truck' probably has some parasitic draws on the battery like a clock, red LED security light?, engine computer, etc.

    I'd probably be looking at a 10W panel for serious battery maintenance under your conditions - Latitude of 27 and probably cold .....

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,288 PostsLatest Activity: Jan 09, 2022