The battery compartment is on the back of the Billy DX machine’s handle. To open it, undo the screw using a Phillips screwdriver and lift off the cover.

Then carefully prise the battery out of its housing.

Check the battery for any obvious faults. If it is leaking or swollen, you should dispose of it and install a replacement. If the battery looks okay, you can test its charge using a multimeter set to DC voltage mode.

Place the multimeter’s positive red probe against the positive terminal of the battery. The negative black probe should be placed against the negative terminal. Here, we can see a reading of 3.4 volts. This is below the battery’s nominal voltage of 3.7 volts stated on its side.

If the battery has a voltage below its stated value, first try to charge it for longer. The voltage should be higher than its stated figure. If the battery cannot reach the stated voltage or its voltage drops after a short use, you may need to replace the battery.

But first, check the battery terminals. These can be affected by dirt, oxidation, or corrosion. This may also have caused power connection problems.

Prise out the terminals using a suitable tool. A flat-headed screwdriver will be fine. You can use another screwdriver to lever against to make this easier.

Starting with one of the terminals, use an alcohol swab to scrub around every surface of the terminals.

You should also clean inside the plastic housing where the terminal sits. Use a screwdriver to push the swab into every corner. Use a lint-free cloth to ensure that the area is completely dry.

You can then slide the terminal back into place. Then repeat this for the other terminal.

Carefully press the wire back into its recess using a flat-headed screwdriver.

You can now check whether the Billy DX machine is working properly.