These type of chargers use temp to determine when to shut off.
They use either a temp sensitive switch or a temp sensitive resistor. The third contact on the battery pack is connected to the temp sensor device. If you have an old useless pack for your Makita, you can open it up and retrieve the temp sensor stuff and perhaps use that to make some sort of temp sensor that you connect to your pack that you want to charge. Not the fastest charger, but it will most likely work.
Just an idea.
/Magnus