You must only open or attempt repairs of CEL products entirely at your own risk. CEL cannot be held responsible for any damage to persons or property which results from your actions.
If you suspect that the fault is a broken connection between the cells. The PH03 is made up of 15 cells x 1.2V each. They are joined using strips of metal which are spot welded onto the cells in series to make up the 18V pack.
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Work on a wooden or non conductive surface with no screws or loose metal items around.
If any liquid or powder is leaking from the cells you should discard the entire pack. This substance can burn eyes and skin, clean up well and do not touch your face.
Carefully open the POWERhandle (remove the direction slider first) and peel off the red paper which caps the cells top and bottom you will see all these spot welds.
You should pick at each one to ensure they are firmly connected, you may find that one or more are loose. This would make a weak connection that may allow some current to pass but under any load they would just heat up and block the flow of current.
To reconnect a tab to a cell:
Scratch the cell surface a bit to help the solder grip the top of the cell. The solder should not pass around the corner of the cell, only on the circular face, contact between the cylinder face and the circular face may cause shorting.
Heat your soldering iron so it is very hot and hold it on the circular face of the cell until the solder flashes (runs freely) across the surface. The surface of the cell needs to be very hot to create a good bond between the tab and the cell.
Heat the tab and apply some solder to it as well, the tab will heat quickly and easily. Press the tab onto the circular face of the cell and melt the solder of both together.
Keep the tab in place using a thin screwdriver or similar until the solder cools. Test the connection is firm by pulling on it.
Repeat for any other loose connections.
Test the voltage of the entire pack. You should see close to 18V DC, if it is less than 15V then there may be a break still or perhaps a failed cell.
You can also test each cell by pressing your tester to each end. You should see between 1 and 1.4V for each cell.