Mastervolt Charge Mate Pro 40 Electronic Charge Relay

The Mastervolt Charge Mate Pro 40 electronically limits secondary-bank charging to 40A, with reverse current blocking and IP65 electronics.

Forty amps is the smaller Charge Mate Pro against the 90A version, and the limit is chosen by what the secondary bank should be allowed to take. That is a different calculation from alternator size. The point is capping what the house bank draws so the starter battery is not left waiting, and a lower cap protects the starter more firmly.

Limiting to 40A can also protect an alternator that would otherwise be worked hard by a large depleted bank. A modern alternator running at full output continuously on a hot engine is being asked for more than it can sustain.

The solid-state design has very low voltage drop and automatically blocks reverse current, so a higher-voltage secondary cannot feed back to the primary. Multiple chemistries including lithium are supported, with LED status indication, IP65 electronics, a corrosion-resistant housing and remote control capability. Explore more battery charging accessories.

• 40A cap, against 90A on the larger version
• A lower cap protects the starter more firmly
• Also protects an alternator from a large depleted bank
• Solid state with low drop and reverse blocking