Not sure if my coments here will add much to the discussion, but like most others, I have given up using Ni-Cad powered gear. However, the frustration is that the tools themselves, though old, are invariably excellent, so I'm attempting to convert them to either Li-ion or if they are 12V adapting them to run with leads off the vehicle battery.
The former is frequently a PITA because rarely do the batteries fit inside without modifying the existing cases. Also because the charging profiles are different, they require either a new motherboard or some form of external charging device and it is critical to use the correct type of charger.
An example is a pair of Einhell cordless drivers - superb quality. I have hard- wired one to work from the car battery, but the other now has 3 X 18650 batteries. A new motherboard is unobtainable and building one is beyond my simple bush brain so the batteries have to be hard wired to the contact plates. To recharge, the battery pack must be removed and connected to a charger. Now comes the tricky bit - which charger?
I've ordered a DC-to-Dc "hobby charger" on Crapbay and if you believe the blurb, the charging profile can be adjusted. It seems the intial charge voltage must be set just slightly above the actual battery voltage for the first phase, then changed to constant current to bring the batteries up to 12.4 volts (or whatever) so they will be fully charged.
If that works, I'll convert a couple of 18V Ni-Cad tools over to Li-Ion.
Please feel free to tell me I'm wrong about any of this, preferably before I burn down the shed