As a general rule, Ni-Cad batteries are good for about 300 charge cycles(completely flat to fully charged), provided one or more of the individual cells in the battery pack do not deteriorate more rapidly. It looks like you derived good longevity from your Bosch.
The Li-ion should do better than that, but as you say, it depends on the amount of charge in the battery when stored for long periods of disuse.
Have you considered converting your Bosch for use as a “corded” drill with a car battery? Open the battery case, remove all the cells (but take care to keep the contacts in the correct position - you may have to use an epoxy resin to do so) and drill a hole in the case for the two-core wire. Solder or otherwise attach the wire to the two contacts (there may be more than two - the others are for temperature regulation or monitoring), and re-assemble the case.
Put car battery terminals on the other end of the wires - remember to observe polarity - and you will be able to use the drill for many more years, even with a weak car battery. I used one for years, until it was stolen.
And it need not be a car battery either - a smaller, sealed 12V battery will do, and you can charge it with your car charger, or even asolar charger.