This guide explains how to test the voltage of your Foil Drive battery, charger and Battery Management System (BMS) using a multimeter.

The process can be used across the Foil Drive battery range, including Assist, Assist PLUS, Gen2 and Gen2.5, as well as compatible 28V and 40V chargers.

Voltage testing can help identify potential issues with the charger, battery or BMS when the charging system is not behaving as expected.

Potential Charging Faults

This test may be useful if you experience symptoms such as:

• The charger is connected to mains power and displays a solid green light, but remains green when connected to a drained battery.
• The charger displays a flashing green light when connected to the battery.
• The battery does not appear to be charging as expected.

Instructional Videos

Gen2 Battery - Voltage Testing

Assist PLUS Charger & Battery - Voltage Testing

What You'll Need

• Multimeter
• Foil Drive charger
• Foil Drive battery
• Small paper clip or similar item, if required to access the BMS test point

Safety

Take care when testing battery and charger voltage.

Ensure the multimeter is set correctly to DC voltage before testing.

Do not allow the positive and negative terminals to contact each other, and take care not to short the battery terminals with the multimeter probes or any other object.

If you are unsure about performing these tests, contact Foil Drive Support for assistance.

Gen2 Batteries

Set your multimeter to DC voltage (V⎓).

Depending on the multimeter, this may be represented by:

• V with a solid line and dotted line underneath — DC voltage
• V with a wave symbol (~) — AC voltage

Make sure you select DC voltage, not AC voltage.

If your multimeter requires you to select a voltage range, choose a range that can measure at least 40 V DC. A 40 V battery can measure above 40 V when fully charged, so do not select a range that is too low.

Testing the Battery Voltage

1. Locate the two large battery terminals.
2. Place the red probe on one terminal.
3. Place the black probe on the other terminal.
4. Make sure the probes remain separated and do not touch each other.
5. Ensure the probe tips are making good contact with the sides of the terminals.

A correctly charged 40V battery should show a voltage reading appropriate to its current state of charge.

For example, the battery shown in the instructional video measures approximately 39.7 V.

If the Reading is Negative

Don't worry if your multimeter displays a negative voltage.

This simply means the probes are connected in the opposite orientation.

For example:

• Red probe on positive / black probe on negative = +39.7 V
• Red probe on negative / black probe on positive = −39.7 V

The voltage value is the same; only the polarity has changed.

Important: Take care when positioning the probes. Do not allow the positive and negative probes to touch each other, as this can short the battery terminals.

Assist and Assist PLUS batteries

Testing Battery Voltage

1. Set your multimeter to DC voltage (V⎓).
2. Place the red probe on the battery positive (+) terminal.
3. Place the black probe on the battery negative (−) terminal.
4. Record the voltage displayed.

Important: Take note of the battery voltage reading. You will compare this with the BMS voltage in the next test.

In the example shown in the instructional video, the battery measured approximately 27.98 V.

Testing BMS Voltage

The BMS test allows you to compare the voltage being measured at the battery cells with the voltage being reported through the BMS circuitry.

1. Place the black multimeter probe into the small hole between the two larger holes on the connector.
2. If your multimeter probe is too short to reach the contact, a small paper clip or similar item can be used to extend the probe.
3. Place the red probe on the positive (+) terminal.
4. Record the voltage displayed.

Compare this reading with the battery voltage measured in the previous step.

In the example shown in the video:

• Battery voltage: 27.98 V
• BMS voltage: 27.98 V

The matching readings indicate that the BMS voltage reading corresponds correctly with the battery cell voltage.

If there is a significant difference between the battery voltage and BMS voltage, stop testing and contact Foil Drive Support for assistance.

Testing the Charger Output

1. Set your multimeter to DC voltage (V⎓).
2. Connect the charger to mains power.
3. Place the red multimeter probe on the positive (+) output.
4. Place the black multimeter probe on the negative (−) output.
5. Record the voltage displayed on the multimeter.

For the charger shown in the instructional video, a reading of approximately 33.4–34.7 V is within the expected output range.

Note: Charger output voltage varies depending on the charger model. Always use the specifications applicable to the charger being tested.