Nerd Battery Post

 

Back in November I mentioned Ken had given me a old lithium battery which I disassembled to salvage the useful 18650 cells.   There were 60 cells and during the last two months I’ve been testing each cell with my special battery tester.  The tester charges, discharges and recharges one cell every 24 hours.  This provides me with the actual residual capacity of each cell.   A new cell has a capacity of 2400mA and those I’ve recovered from the battery range between 2359 to 1806mA.  No battery retains full capacity after use.  Each cell has received new shrink wrap cladding and insulated washer around the positive terminal.

 

None of the cells were dead which left me wondering how to use them.  I decided to make some batteries for my DeWalt power tools.  I have more tools than batteries and find myself swapping batteries.   This situation occurred because the batteries are expensive and obviously I don’t use all the tools simultaneously.   An 18V 4Ah DeWalt battery cost $200.

 

After searching on Aliexpress I ordered two kitset batteries (less cells) and a portable spot welder.  The kitsets were $21 each and the welder $80.  For an outlay of $140 I should be able to make two batteries which would have cost me $400 from a tool store.

 

My batteries will be 18V with 4Ah capacity.   The cells need to be configured as 5S2P (two rows of 5 cells in series).   Each cell has a voltage of 3.7V so five in series is 18.5V   It is important that each row has a similar capacity.  To achieve this I created a small spreadsheet.  By shuffling the cell capacities on the spreadsheet I was able to achieve the desired result.  The rated capacity of each battery was approximately 4.6Ah.

 

It only took 10 days for the battery kitsets to be delivered.  Interesting to note the EU and UK representatives on the package label

 

The other interesting piece of information was the naming of the battery.   One assumes this is a effort to avoid breaching DeWalt copyright.

The cases looks very similar .  Importantly, it fits my DeWalt tools

Inside each case were a printed circuit board, cell holder, screws and decals

No instructions!!

I needed to do a test fit of the cells and printed circuit board to ensure I had the cells correctly orientated.  The nickel strips were then added and held in place with a rubber band.

I then soldered the Tabs on the nickel strip to the board

I probably made a mistake here.  Before soldering the Tabs I should have soldered the battery indicator wires to the circuit board.

 

With poor eyesight and shaky old hands the subsequent soldering of the indicator wires proved to be problematic.

The board and cells were then removed from the case so I could spot weld the nickel strips to the ends of the cells.

I’ve never welded and this was a learning experience.  The spot welder is portable and powered by a rechargeable lithium battery.  Each cell needs four spot welds at either end.  It took a significant number of attempts to establish the required welding settings.  Too low and the nickel strip doesn’t weld to the cell.  Too high and a hole is blown in the nickel.  Working my way up through the power setting I established the setting 10 appeared to work.

My little spot welder

After establishing the correct settings the welding went rather quickly.

The cells and circuit board went back into the where I then tested the terminals to see if the connections were working

19.97V for an 18V battery.  Everything looks good.

The battery indicator wires were soldered and the top screwed into place

I fitted the battery to my DeWalt drill and tested it worked.   Now I need to assemble the second battery.