Charging the truck battery with solar- will a 1.5W panel do?

[Sentinelist]

Correction: I have two batteries (recent DuraLast Gold FLAs), and two 1.5W solar panels connected to each respectively with battery clips. They're just not doing the task, and I have them on my dash in heavy sunlight during the afternoon for at least 4 hours, west facing. They're velcro'd to the dash, not suction cupped to the windshield (about to do that). Did I buy the wrong panels? Do I need more power? The batteries are draining - even without the camper plugged into the truck now! - after just a few days. Maybe I have battery problems, though they tested good at AutoZone late last year. A trickle charge battery tender on a long extension cord resolves the trouble and then the batteries have no trouble cranking. Thoughts?

[narcodog]

I can relate to the computers drawing down your battery's. When I bought my 03 Chevy I would not drive it for weeks at a time. When I would go to drive it the battery was dead. I took it to the dealer they did all sorts of tests and everything was fine. They put a big battery in it still did not fox the problem.
After I retired and I drive the truck more often, well no more dead battery problems.

[tempforce]

if your vehicle has a computer in it. the computer will draw down the batteries in a few weeks. if the draw is large say batteries drain in less than two weeks something is wrong..
i agree, you need larger solar panels to keep the system charged.
i use a little fence/gate solar panel on my old ranger... it has -0- electronic loads..

[Sentinelist]

Thanks, all. It sounds like I have a parasitic draw- I just chased one of these down in another of my vehicles last month so I'm well versed! I'll start there. After I take these puny panels back to Harbor Freight... I'm now looking at a couple good 10W panels rated highly on Amazon that I can replace them with on my dash with a charge controller each. Of note, the batteries are actually already running in parallel. I'm assuming with a charge controller on each, it won't be an issue interfering with that.

The goal is to be able to walk out after 3 months (or something) and have the trunk crank right up.

Separately, I'm about to setup 200W of solar on top of the camper with a 30A controller and a separate battery bank (see earlier thread today regarding my Lance for install spaces). I'm hoping to use a battery isolator to tie these two together better than the camper's 7-way plug that currently connects it to the truck with a single marine battery and just drains the snot out of my truck batteries. Solving problems by complicating them!

[hmknightnc]

If they are draining to where they won't crank the truck after a few days without the TC plugged in the batteries are failing or you have a pretty significant parasitic draw (short somewhere). The batteries just sitting in truck should last several months. Start chasing down that short

To answer your question directly - for large batteries use 10watts per battery if not using a controller.

[time2roll]

I recommend 5 watts to 10 watts per battery. If you have parasitic loads then aim for the high end.

Better to get 40 to 100 watts and a small controller.

[Mandalay_Parr]

Probably way too small. 12 watts would equal about 1amp with no losses.