The MT1 Multi2PRO runs between 9 and 12.4 Volts and the battery is made up of 3 cells each with a nominal voltage of 3.6V. The most common fault is loss of balance between the 3 cells, typically found by measuring each cell individually. Anything lower than 3.0V per cell indicates a failed cell which would need replacing. So if you measure the voltage of the whole pack of 3 cells and get a reading of 9.0V or less then you can be pretty sure that the pack has a bad cell.

At this point the pack needs to be replaced. It is not advisable to just replace a single cell as the cells used to make the pack should be matched.
As these battery packs are no longer available there are a few options which you could attempt at your own risk as follows:
  1. Run the tool from another 12V DC source. 12V is a common voltage so you may already have an transformer or suitable battery to provide the power. Connecting this to the two terminals visible where the battery fits inside the tool would allow the tool to run.
  2. Replace the cells inside the battery. A warning about this; high current present even in faulty batteries can cause nasty burns or fire. Separating the cells from the electronics requires care to avoid damage and shock. Cells are spot welded to the conducting wires, soldering is possible but takes some skill and time to heat the cell surface. Only a skilled and competent person should try this and the risk is entirely their own.
    Opening the battery requires it to be squeezed to release some clips not visible on the outside. To open the battery case up, squeeze the endcap in a vice on the front and rear (the sides that do not have the green release latches), this will unlock the internal catches which hold the shell together without much pressure required. When you put the shell back together make sure you press the green catches in on their springs, otherwise they can break off. Do not squeeze more than 10mm to avoid damage the the parts inside. Once squeezed the rear cap should come free. The cells are a very common shape called 18650.
  3. Buy a different tool. Our mains powered Multi-tools are great value and there are also some new battery versions. Typically your existing blades will work with some exceptions.