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Van Mounted Systems - Charging & Maintaining your battery

How to charge the battery on your Window Cleaning system is something to consider before making a purchase. There are three common option and each is highlighted below.

For an introduction to lead-acid leisure batteries and how to maintain them, read our guide to maintaining Window Cleaning system batteries

Leisure Battery Smart Charger

Avon smart battery charger - window cleaning systems

This smart charger is designed to connect to a mains power source and requires you to remove the battery from your Window Cleaning System. The Avon Leisure Battery Smart Charger automatically detects the battery voltage and condition before diagnosing, charging, and reconditioning.

It maintains the battery in multiple stages: bulk stage (maximum voltage and current), absorption stage (constant voltage with decreased current), and float stage (constant current with slightly reduced voltage). This multi-stage process ensures fast and efficient charging that extends battery life.

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Split Charge Relay

split charge relay - window cleaning systems

Most Window Cleaners will have the system battery linked to the vehicle battery either using a split charge relay or a Battery to Battery Charger (covered in the next section).

In simple terms, this means that every time you run your vehicle, the leisure battery in your Window Cleaning system will charge. Providing you cover enough mileage, you won't need to touch the battery or charge it externally.

It's important to note that the type of driving, vehicle and mileage will effect how much charge is actually put back into the battery - in some circumstances you may still need to charge it externally. Fortunately all systems have a means to read the battery voltage on the controller in a few seconds.

With regular monitoring you'll eventually get a feel for much charge is used and put back in each day. Use the table in our battery maintenance guide to assist with this. This method involves connecting the battery charging circuit to the vehicle alternator. When the engine is switched on, the battery goes into charging mode.

Split Charge Relays can be found in two subtypes, though voltage sensitive is the only option we supply. The two available options are:

Ignition-Triggered Relay: A simple setup where the battery charges immediately when the ignition is switched on on a DC signal. This is not a recommended charging method as there is no proper voltage compatibility and nothing to stop the battery overcharging.

Voltage Sensitive Relay: An alternative to the ignition-triggered relay and the only one currently supplied by Window Cleaning Warehouse. This version is sensitive to the battery voltage and will automatically cut off when the battery reaches 13.7V DC.

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Battery to Battery Smart Relay

Battery to Battery Charger - Window Cleaning Systems

Battery to Battery (B2B) chargers or smart relays are the preferred option for modern smart-alternators. which operate in a slightly different way to what is found on older vehicles. These smart alternators reduce the charging voltage once they sense the vehicle battery is fully charged, meaning for significant portions of your journey, no charging is taking place. Because of this, the voltage varies quite and is generally inconsistent compared with older alternators This is covered in more in our guide to smart alternators and how they effect your Window Cleaning system


To stop this having an effect on the Window Cleaning system battery, B2B Chargers either increase or decrease the voltage to provide a balanced and stable charge. These are a more expensive option than a split charge relay but generally you will find that they provide a faster and more reliable charge, with greater protection for both batteries.

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Choosing the Right Option for your Vehicle

Split charge relays have long been a favourite for Window Cleaners, though as vehicle technology progresses it is becoming more and more necessary to use a battery to battery charger. These are the circumstances with which we recommend to do so:

  • If you are purchasing a new vehicle, all new vehicles will now have smart alternators fitted as standard and eco-models often have regenerative breaking which will contribute even more to uneven charging.
  • If your vehicle is a few years old then look out for Euro 5 or Euro 6 emissions compliance, which often indicates a smart alternator. 
  • If you are also using a Window Cleaning System with a large draw on the battery, through hot water or multiple powered hose reels for example.
  • If you have a compact round with few miles between jobs