Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2)

I have had a Hitachi DB3DL2 ‘pencil’ type cordless screwdriver for about 12 years, and one of the supplied two batteries (EBM315 1.5Ah) has just failed. This is not the first failure, the charger failed after about five years use and the LED push button became electrically leaky flattening the battery so the push button was removed. The second battery is still working, but at about 65% capacity.

It is actually a really good tool to use, and so worth trying to extend its life. To that end:

  • I purchased a new genuine Hikoki (new name for Hitachi -Koki) charger on Aliexpress for about $80 shipped (they are more like $150 locally);
  • I purchased an after market EBM315 1.5Ah battery on Aliexpress for about $25 shipped;
  • I purchased locally two Panasonic NCR1650B unprotected 3.4AH 18650 cells to repack the two original batteries; and
  • repacked the failed battery.

Above is a capacity test of the new Aliexpress 1.5Ah battery and the working 14 year old Hitachi battery. The little squiggles are concerning, to be further investigated. It is my experience that most rechargeable batteries purchased on eBay and Aliexpress grossly fail to meet specified capacity, the one is a welcome change… though note the quite low cell voltage to achieve rated capacity.

This article might assist readers considering repacking the EBM315.

First some pictures of a disassembled batteries for planning repack.

Above, carefully remove the three small self tapping screws in the end cover to release it and the spring from the battery. The screws were very tight, be careful to not damage the heads.

Above is a view of the battery internals, the safety shutter covers the -ve terminal.

Above, there is some kind of temperature sensing bead secured with adhesive, it can be peeled off with care. Likewise, the rubber pads can be peeled off for reuse.

Above is a view of the battery pack terminals (the plastic tray is to support the parts for the pic).

Suggested steps:

  1. Carefully cut the nickel strip from the main -ve terminal (lower right) to the cell -ve terminal (this allows the -ve terminal to be lifted out of the insulator piece to give better access to the +ve terminal).
  2. Lift the small square of Elephant Hide / Barley Paper covering the cell +ve terminal.
  3. Carefully cut the nickel strip between the main +ve terminal (upper left) to the cell +ve terminal (I have used a very small engraver’s burr, and on another, a pair of pliers to pry the strip off the cell contact).
  4. Disassemble the parts and remove the ends of the nickel strips from the +ve and -ve terminals (I used a small grinding stone to grind down the spot welds, remove the strips and grind the terminal surface flat to receive new strips.
  5. Weld the new 7×0.05mm (I used 0.2mm) pure nickel strips to the terminals.
  6. Reassemble the parts and weld the nickel strips to the +ve and -ve cell terminals.
  7. Reapply the other parts (including the small rectangle of paper insulation – little dob of hot melt adhesive was used).
  8. Fit a short length of thin heatshrink (23mm dia, 0.1mm wall thickness) over the temperature sensor and rubber pads and shink it minimally to hold the parts in place.
  9. Reassemble and test the battery pack.

I would select pure nickel because this is a high current application, then verify that what you receive is nickel, not nickel plated steel. In this case I performed a quick test with a cutoff wheel in a dremel, no sparks is good.

This is a lot of work, and hardly worthwhile if the Aliexpress batteries proved to be good in the longer term, but I am confident that the repacked batter will be good in the longer term and will repack the other original battery shortly.

I repacked the second original battery a couple of weeks later, again a Panasonic NCR1650B unprotected 3.4AH 18650 cell was used and the operation went smoothly.