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Choose a solar charge controller for a backup battery

By the Plain Prepper editors. Updated 2026-10-18.

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Quick answer

A charge controller sits between solar panels and a battery and keeps the battery from overcharging. Small 12V setups can use a PWM controller such as Renogy's Wanderer 30A, which accepts up to 25 V from the panels, or the IP67 waterproof Voyager 20A. Larger arrays need MPPT: Renogy's Rover Li 40A accepts 15 to 100 V and Rover 60A up to 140 V. Victron's SmartSolar MPPT line adds a load output and a 5-year warranty. Always keep your panels' open circuit voltage below the controller's limit.

What a charge controller does

A charge controller sits between the panels and the battery and regulates charging. Renogy describes its PWM controllers as constantly monitoring battery voltage and adjusting the charge so the battery is charged safely, and lists protections against overcharging, over-discharging, short circuits, overload, reverse polarity and reverse current on its controllers.

If you are building a backup system around panels and a battery, see our 100 watt solar panel guide and 12 volt lithium battery guide.

PWM or MPPT

PWM controllers are the simpler type. The Wanderer 30A accepts a maximum of 25 V from the panels, so it suits a 12 V battery with panels wired to match.

MPPT controllers take higher panel voltage and convert it for the battery. Renogy lists up to 99% tracking efficiency and 98% peak conversion efficiency on its Rover MPPT controllers, a 15 to 100 V solar input range on the Rover Li 40A, and up to 140 V on the Rover 60A.

Size it to your panels

Two numbers matter. The rated charge current is the most amps the controller sends to the battery: 20 A (Voyager), 30 A (Wanderer), 40 A (Rover Li 40) and 60 A (Rover 60). The maximum panel input voltage is the most the panels can feed it: 25 V (Wanderer), 25 V at 12 V or 55 V at 24 V (Voyager open circuit limits), 100 V (Rover Li 40) and 140 V (Rover 60).

Renogy says to make sure the open circuit voltage and short circuit current of your solar panel set are below its controller's limits. Renogy also lists maximum panel wattage: 520 W at 12 V for the Rover Li 40A and 800 W at 12 V for the Rover 60A.

Battery type and temperature

Set the controller for your battery before connecting it. Renogy says it is essential to set the battery voltage first on the Rover, and that on the Voyager you must set the voltage manually to charge lithium batteries. The Voyager supports gel, AGM, flooded and lithium.

Renogy says the Rover 60A ships with an external temperature sensor to prevent undercharging in cold down to -40 degrees F and overcharging in heat up to 149 degrees F, and that the Rover Li can wake a lithium battery whose BMS has shut it off.

Where to mount it

Check the enclosure rating before you pick a spot. Renogy lists IP20 for the Wanderer and IP32 for the Rover 60A. The Voyager 20A is rated IP67 and Renogy says it can run in water spray, rain and condensation, which suits an RV roof or shed wall.

Victron lists load output terminals with a configurable disconnect voltage on its SmartSolar MPPT controllers, useful for running a light or fan straight from the controller.

Warranty

Renogy lists a 2-year material and workmanship warranty on the Wanderer 30A and Voyager 20A. Victron lists a 5-year standard warranty on its SmartSolar MPPT controllers.

What to look for when you buy

Questions people ask

Do I need a charge controller for a solar panel?

Yes, when charging a battery. Renogy lists protections against overcharging, over-discharging, short circuits and reverse polarity on its controllers.

Is MPPT better than PWM?

MPPT accepts higher panel voltage: up to 100 V on Renogy's Rover Li 40A and 140 V on the Rover 60A, versus 25 V on the Wanderer PWM. Renogy lists up to 99% tracking efficiency on its Rover MPPT models.

What size charge controller do I need?

Match the amp rating and the maximum panel voltage. Renogy says your panels' open circuit voltage and short circuit current must stay below the controller's limits.

Can a charge controller go outdoors?

Only if rated for it. Renogy's Voyager 20A is IP67 for spray and rain; the Wanderer is IP20 and the Rover 60A IP32.

Sources

• Wanderer Li 30A PWM Charge Controller (renogy.com), Renogy
• New Edition Voyager 20A PWM Waterproof Solar Charge Controller (renogy.com), Renogy
• Rover Li 20/30/40 Amp MPPT Solar Charge Controller (renogy.com), Renogy
• Rover 60 Amp MPPT Solar Charge Controller (renogy.com), Renogy
• SmartSolar MPPT 75/10, 75/15, 100/15 and 100/20 (victronenergy.com), Victron Energy

Sources checked 2026-10-18.