I will start with an appology to all the Dewalt and Ryobi fans on Instructables but I am a Metabo tools man. I use their 18V Drill, Impact Gun and 4" Grinder. My van was broken into last year and the tools but not the batteries taken. I replaced the tools and ended up with yet more (10) batteries and 6 chargers.

I do some site work, all with my laptop and rarely near a power outlet so I decided to see if all of these extra batteries in my van could come in useful.

Step 1: Get Started

You will need:

At least 1 power tool battery

1 SPARE battery charger (after this 'ible it will never charge a battery again)

1 compatible laptop charger

A multimeter

Knowledge of your laptops operating voltage.

Now time for the warnings....

This instructable may expose you directly to AC electricity, this can and will kill you so be careful

Check all of the voltages and polarities carefully as getting one of these wrong may cause damage to your laptop

Please only do this if you know what you are doing yourself!

Step 2: Strip the Laptop Power Supply

pen the casing on the laptop power supply, you don't need to be very careful as we won't be using it again.

Find where the DC (laptop) side of the power supply is and using your meter confirm the voltage is correct for your laptop and identify the polarity, in my case the wire with the white insulation is positive.

Use your meter to confirm that your battery also puts out a compatible voltage, my laptop needs 19.5Vish, all my tools are 18V but I know that a healthy battery should be above this, my meter confirmed 19.7V

Step 3: Strip the Power Tool Charger

Open the casing on the power tool battery charger carefully as we need it again.

Remove all of the charging circuit and discard it, DO NOT ATTEMPT TO USE IT WITHOUT THE CASING THIS MAY EQUAL DEATH!

Remove the rubber grommet from the power cable as we will use this as the laptop power cable exit.

Following the terminals on the battery, we are only interested in the positive and negative outputs from the battery (not the charging terminals). In this case they are the red (+) and black (-). Remove the other wires to prevent confusion or a short.

Step 4: Pass in the Power Cable

Push the power cable through the grommet, I needed to carefully run a drill bit through it first as my laptop cable is round but the old power cable was 2 core flat!

Connect the positive and negative wires, I use push in 3M terminals, it save on soldering and its stronger than crimp terminals.