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Mastervolt introduces the Charge Mate Pro 90 to efficiently recharge two batteries from one source

The new Charge Mate Pro 90 is an electronic relay that allows a second battery to receive up to 90 A of charge current from a single alternator. Suitable for all battery types, it is ideal for recharging Lithium Ion cells and has built-in safety features. An effective solution for high power demand on board in combination with a need for prioritised or current limited charging.

Mastervolt, the Dutch-based manufacturer of off-grid power solutions, has added a new and more powerful model to its highly successful Charge Mate Pro series of electronic charge relays. The new 90 A model supplements the 40 A version already available, and will quickly and intelligently charge two batteries from just one source when higher charge currents are demanded for, e.g. when charging  Li-ion batteries. When used in parallel they are even suitable for large automotive alternators up to 225 A.

Safety is a priority

When there are two batteries on board, typically an engine start battery and a service battery, the second battery usually requires its own charging solution.  A mechanical relay will charge the flattest battery first, and then switch to the other, but this isn’t always ideal, as it could leave the engine starter battery discharged.

The new Charge Mate Pro 90 works differently, by always prioritising the primary battery whilst still charging the secondary. A very effective solution for charging two batteries from one source, while significantly reducing the risk of a flat battery.

An example would be a bow thruster battery and a service battery connected to the same alternator. The Charge Mate Pro 90 would prioritise the service battery for the bulk of the charge, whilst still feeding current through to the bow thruster battery. Any return current is automatically blocked, even if the secondary battery is of a higher voltage, which helps to keep the bow thruster battery sufficiently charged. The current limiting prevents power dips of the on board electrical network.

In the event of a main battery failure, an emergency start facility is available by means of an optional bypass or ‘battery bridge’ switch.

Built to last

Mastervolt is the official supplier to gruelling yachting events such as the Volvo Ocean Race because the products are built to last, and the Charge Mate Pro 90 is no exception. Designed for the harsh marine environment, the relay is suitable for all types of battery chemistry and alternators, and the electronics are rated to the demanding IP65 standard.

The relay is housed in a corrosion-resistant housing flanked by two heat sinks, and its operation can be monitored via built-in LED indicators. The unit includes automatic battery detection, so it can work seamlessly with either 12 V or 24 V systems.

The Charge Mate Pro 90 adds to the existing model line-up, and offers a unit that is easy to install and meets the demand for prioritisation or current limitation.


  • Makes effective dual charging possible.
  • High system reliability by prioritised charging of the main battery.
  • Fast and easy installation.
  • Suitable for all battery types, including Lithium Ion.
  • Charge current to secondary battery limited to 90 A.
  • Return current blocked under all circumstances.
  • Prevents power dips of the on-board electrical network.
  • Works with all types of chargers and alternators.
  • IP65 electronics in a corrosion resistant case.
  • Monitoring via LED status indicator.          

Technical specifications:

  • Model: Charge Mate Pro 90.
  • Type: electronic relay with low voltage drop of 0.2 V max.
  • Size: 157 x 140 x 80 mm (6.2 x 5.5 x 3.1 in).
  • Weight: 0.88 kg (1.9 lb).
  • Input voltage: 9 – 32 V.
  • Battery voltage: automatic 12/24 V detection.
  • Battery types: all chemistries.
  • Output current: limited to 90 A (derating above 25 °C).
  • Switch on voltage: 13.5/27 V after 5 sec (12/24 V).
  • Switch off voltage: 12.75/25.5 V after 2.5 sec (12/24 V).
  • Number of batteries: 2.
  • Remote switch functions: On, Off, Auto, Start assist.
  • Parallel operation: yes.
  • Protection degree: IP65.
  • Ambient temperature: -40 °C to 60 °C.
  • Approval: CE.
  • Connections:
    - 3 x fast-on connectors (switch, ground and status).
    - Switch: offers an optional single pole switch for remote operation.
    - Status: for an optional LED indicator.