Start with your battery size
- 20A: good for 50 to 100Ah batteries and simple setups.
- 25A: a great all-rounder for 100 to 200Ah.
- 40A: best for 200Ah and up, or if you need to recharge fast on short drives.
Other things that matter
- Alternator type: smart (variable voltage) alternators need a charger that supports them, usually through an ignition wire.
- Cable run: more amps over a longer run means thicker cable. A 40A charger running to a caravan needs much heavier cable than a 20A charger under the bonnet.
- Solar input: many DC-DC chargers include an MPPT solar input, which can save buying a separate controller.
- Mounting spot: check the charger's temperature rating if you're mounting it in the engine bay.
Gear picks
Twin-core battery cable
- Sized for your charger and run length
- Auto-grade insulation
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