Disclosure: I work with SolarBatte, a UK shop for a simple solar trickle charger for 12V batteries. This write-up is based on how we set the panel up for cars, caravans, motorcycles and boats left standing.
Why this is a wiring / maintenance check, not a “big solar install”
Stored vehicles still draw a small parasitic load (alarms, immobilisers, ECUs). A flat battery is usually a maintenance problem, not a reason to fit a roof array. A small daylight panel with a controller that covers reverse current and over-charge is enough to offset that drain when the vehicle sits on a driveway, in a compound, or at a marina without a socket.
The three connections I always check
- Panel in daylight — suction cups on glass, or any secure daylight spot. Shade kills the red “enough sun” cue.
- Battery side — alligator clips on the 12V posts (red +, black −), or the cigarette-lighter plug if that circuit is live with the key out.
- Lamp cues — red ≈ enough sun on the panel; green ≈ battery connected and charging path closed.
If green never appears, I re-check polarity and whether the lighter socket is actually powered when parked.
What I do not expect it to do
It maintains a healthy 12V battery; it is not a recovery charger for a deeply discharged pack. If the battery is already flat, recover it properly first, then leave the panel on for storage.
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