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)?

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 .....

New battery should need less power. Stick with 2.4 if that is working.

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

I have been using a Coleman CL-600 solar panel, 600ma, 15V, 9Watt, for about 5 years now. I have 2 panels: one for V10 starting-battery, and the other for the pair of 6V Trojan T105's.MH is stored for 5 to 6 months with only the solar-panels. I check monthly and run engine, and generator (if temperature is around 20F or higher). Done to exercise both as needed. I always check batteries with volt-meter before starting engines. They are always found at full charge.It should be noted that I have no currents drawing down batteries. If you have a radio with digital displays drawing current continuously you will need 5 or more watts.

smkettner wrote:New battery should need less power. Stick with 2.4 if that is working.This.If your new battery is AGM, it will be just fine over 3-4 months if first fully changed and then disconnected....or connected to the small solar charger.The self-discharge in an AGM is almost negligible.

Size of solar maintainer for car battery? | Good Sam Community

13 Replies

dclark1946
Explorer
Nov 18, 2015
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
time2roll
Nomad
Nov 18, 2015
New battery should need less power. Stick with 2.4 if that is working.
Ed_Gee
Explorer II
Nov 18, 2015
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 .....

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Size of solar maintainer for car battery?

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