Since starting this thread I’ve continued to use NiMH AA cells. For my homebrew CW rig I use 10 in an external holder and for the occasional use of the FT817ND I use 8 in its internal holder. This has been successful so I haven’t really felt the need to upgrade to lithium cells of any sort. Every now and again I looked at getting Lipo but didn’t want to invest in a new charger as well as the battery. I wasn’t sure whether I should get 3S or 4S worrying that the former wouldn’t be high enough voltage for the full 5W from my homebrew rig and the latter would be too high a voltage. LiFePO4 was another option with 4S being the ideal voltage but it seems to be impossible to buy a suitable battery at a sensible price since Hobby King closed its UK warehouse.
My wife was given a small USB power bank a few years ago. We didn’t use it much and then I found it didn’t work at all. Eventually I decided to take it apart and found a single 18650 cell. This was generating exactly 0V. A bit of research showed that its CID must have tripped. This is the safety device that disconnects the cell if there is a build up of pressure. It is possible to reset them but since it tripped due to high pressure this is not a sensible thing to do. I put the cell and the power bank to one side and forgot about it.
We’ve got an old netbook with 2 batteries and an old laptop. We don’t use them and the last time I tried either, none of the batteries would charge up. A couple of weeks ago I decided it was time to take apart the high capacity battery from the netbook. Inside were 9 18650 cells in 3S3P form along with a BMS board. A quick check with the multimeter showed 2 parallel sets were just above 2V and the other was much lower - either about 1.3V or 1.7V, I can’t remember. I cut apart the cells but I didn’t have a charger so what to do now? I didn’t want to invest in a charger only to find none of the cells were any good.
Then I remembered the power bank. I could use it to charge one cell at a time. I charged up 3 and they got to about 4.13V each so it was looking good. I soldered them together (they still had their spot welded tabs) to make a 3S battery and connected it to the rig. I had it sat on my desk and did some SOTA chasing. I was pleased to see that the power output was still good. I kept a careful check on the voltages so that I didn’t over discharge the cells. It kept the rig on receive for hours and continued to transmit too. So it looked like there were enough cells to make at least one viable battery pack.
The cells are marked CGR18650E which are Panasonic 2550mAh cells. The datasheet says to charge to 4.2V at 1700mA and discharge to 3V. I bought an Imax B6AC charger and set about testing the cells by charging and then discharging each one. This showed the capacity of each cell was between about 1650 and 1800mAh. The cells are old and have been through many cycles and then left to slowly discharge but I was hoping for a better result, especially since my AA cells are 2000mAh.
The Li-Ion program on the B6 charger only charges to 4.1V. It seems this only applied to early cells and all modern cells are 4.2V. So I switched to the Lipo program and retested. I have now been through all 9 cells and they vary from 2079 to 2179mAh which I think is pretty good. They are over 15 years old!
From eBay I got a 3 cell holder and a voltage monitor. I already had all the bits to crimp a balance connector. I followed @G4TJC’s advice at G4TJC: 18650 Lithium Pack and made up a pack much like his. I used it on my activation last week. When I got home I charged it up again and it took 500mAh. The activation was about 1.5 hours so it seems like the pack could last for 6 hours.
With 2 more batteries to take apart it looks like I should be able to get plenty more cells for more packs. 4S is still an option although I may have to make some mods to the rig but it would mean higher output power. I can also ensure future rigs will work at higher voltages.