A solar trickle charger keeps a 12V battery topped up while a vehicle sits unused, by replacing the small amount of charge it loses each day. It's ideal for a car, motorcycle, boat or tractor parked outdoors for weeks at a time. What it can't do is recharge a flat battery quickly, and it can't work in a dark garage, which is where most motorcycles spend the winter.
What a solar trickle charger does
Batteries slowly lose charge on their own, and many modern vehicles also have a small constant drain from alarms, trackers and electronics. Over a few weeks that can leave a battery too flat to start the engine, and lead-acid batteries left flat for long are damaged permanently. A small solar panel puts back a little charge every day and keeps the battery healthy.
The garage problem
A solar panel needs daylight. Behind a windscreen or on a dashboard it gets some, outside on a boat or caravan it gets plenty, but in a closed garage it gets almost none. If your motorcycle or classic car spends the winter in a garage with a socket, a mains battery optimiser is the better tool: it's cheaper to run, works day and night, and manages the battery more carefully. Solar is the answer when there's no mains power - an outdoor bike, a boat on a mooring, a car on the drive, farm machinery in a field.
| Situation | Best option |
|---|---|
| Motorcycle in a garage with a socket | Mains optimiser |
| Car parked outside for weeks | 5-10W solar on the dashboard or bonnet |
| Boat on a mooring | 10-20W panel with a charge controller |
| Tractor or machinery in a field | 10-20W panel with a charge controller |
| Completely flat battery | Mains charger first, then solar to maintain |
What size panel?
For maintaining, not charging, you need very little. 5 to 10 watts covers most cars and motorcycles. 10 to 20 watts suits a boat, a leisure battery or a vehicle with a bigger drain. Panels above roughly 10W should be used with a charge controller, so they can't overcharge the battery in strong summer sun. Many kits include one. For a yacht or dayboat that needs more than maintenance, see our solar panels for boats guide.
Connecting it
- Crocodile clips or ring terminals on the battery are the most reliable connection
- Cigarette-lighter or OBD plugs only work if the socket stays live with the ignition off - many modern cars switch it off
- Motorcycles usually need a permanent battery lead, such as the ones supplied with optimisers
- Lithium batteries need a charger that supports them - check before connecting
Recommended chargers
Everything below was in stock on Amazon UK when this guide was written.
Oxford Solariser OF949
Oxford's solar maintainer for 12V batteries, from one of the best-known UK motorcycle accessory brands. It shows by LED when it's charging. Rated 4.4 stars from 698 reviews.
amazon Check Price on Amazon →POWOXI 7.5W solar battery maintainer
The most-reviewed solar trickle charger on Amazon UK, with over 6,400 ratings averaging 4.4 stars. It has a built-in charge controller and a diode to stop it draining the battery at night. It suits a car or van parked outside.
amazon Check Price on Amazon →Topsolar 20W panel with 10A controller
A 20W panel with a proper charge controller, enough for a boat, leisure battery or tractor. Rated 4.4 stars from over 3,600 reviews. For a smaller job, the Topsolar 10W (~£25) has over 2,600 reviews.
amazon Check Price on Amazon →CTEK XS 0.8 battery charger
A mains optimiser designed to stay connected for months, ideal for motorcycles and other small batteries over winter. Rated 4.7 stars from nearly 1,500 reviews. For cars, the CTEK MXS 5.0 (~£80, 9,600+ reviews) is the standard choice.
amazon Check Price on Amazon →OptiMate 1 Duo
A compact mains maintainer for motorcycle batteries that works with both lithium and lead-acid types. Rated 4.8 stars from 918 reviews.
amazon Check Price on Amazon →Summary
- A solar trickle charger maintains a battery - it won't revive a flat one
- 5-10W for a car or motorcycle, 10-20W with a controller for a boat or machinery
- In a garage with a socket, use a mains optimiser instead
- Plug-in sockets only work if they stay live with the ignition off
- Check the charger supports lithium before using it on a lithium battery
If you need power for more than keeping a battery alive, our guides to portable solar panels and touring caravan solar cover bigger setups.
Frequently Asked Questions
Do solar trickle chargers work in winter?
Yes, outdoors, although they put in less charge on short grey days. Maintaining a battery needs very little, so a 5-10W panel usually copes. Inside a dark garage they barely work at all.
Can a solar trickle charger charge a flat battery?
Not quickly. They are designed to maintain charge. Recharge a flat battery with a mains charger first, then use solar to keep it topped up.
Will a solar trickle charger overcharge my battery?
Small panels of a few watts are unlikely to, and many have a built-in controller. Above about 10W, use a charge controller to be safe.
Does a solar charger work through the cigarette lighter?
Only if the socket stays live with the ignition off. Many modern cars switch it off, so a direct battery connection is more reliable.
What is best for a motorcycle over winter?
If it is in a garage with a socket, a mains optimiser such as the CTEK XS 0.8 or OptiMate 1. If it lives outside with no power, a small solar maintainer.