Sunday, 6 May 2018


You may recall I had “harvested” six 18650 Li-on cells from our old Asus eee netbook computer battery only to discover they were so flat the charger wouldn’t recognise them.  Today I managed to solve that problem with one of the flat cells and have charged it.

My method was to use a second partially charged battery to add some charge to the flat battery.  This resulted in the battery charger “recognizing” the battery and fully charging it.  To do this I needed one partially charged battery; which I didn’t have.  However whilst at the rubbish tip recycling centre yesterday I managed to “acquire” an old Li-on battery for a portable tool.  Upon dismantling the battery I discovered 10 water damaged 18650 Li-on cells.  Fortunately one cell still had a partial charge and I was then able to fully recharge it using the charger. 

Once the cell was fully charged it was connected in parallel with one of the cells from the computer battery.  The setup looked like this…


The voltmeter showed an initial voltage of 4.7V which steadily dropped to 3.7V as some charge from the good cell flowed to the flat cell.  The Lithium cells shouldn’t be connected together more than 40-60 seconds because there is a risk one of the cells might overheat and catch fire.

After 60 seconds I disconnected the two cells and then connected the flat cell to the charger.  Sufficient charge had gone into the cell for the charger to recognise it.


You can see the charger display in the photo below. 



  • Top left – one Lithium ion cell in series
  • Top middle – charging at 1 amp
  • Top right – cell voltage is 4.08V
  • Bottom left – charging cycle
  • Bottom middle – elapsed cycle time in minutes and seconds
  • Bottom right – number of milliamps charge put into the battery

The cell has been charged and is now on a discharge cycle.  The plan is to conduct the charge-discharge cycle three times and establish the capacity of the cell in milliamps.  Hopefully I’ll also be able to recover some storage capacity.  If I can do this for all six of the laptop cells then I will have sufficient cells to make a replacement Li-on battery for my old Panasonic portable drill.

1 comment :

Mrs. Jaqueline Biggs said...

LOL! No wonder you were on a U.N. Peacekeeping force; I do believe you could talk anyone into just about anything! Les would be chuffed to bits reading your blog. He so loved do it yourself projects. Over engineering you say?? Les did the very same thing but he called it "built to last."

Enjoy the more moderate temperatures of winter. We wave had the third straight day in a row hothotHOT! Although I dislike it this hot, I shall forbear for the sake of the British narion. I have lived here 7 years and this is only the second sunny bank holiday weekend we've had. The last one was back in 2013.

Love and hugs to you both,

Jaq xxx