question

Most 18V powertools work with 18V lithium batteries, which need a special lithium charger. This charger can have multiple battery connections, for cell temperature monitoring, or for protection.

A MPPT solar charger can only work with 12V/24V batteries, and only has 2 wires for [+] and [-].

Personally I would not recommend to connect a 18V powertool battery on to the MPPT charger.

Thanks for your quick answer - you are pointing directly at the problems... I cannot assume anything about the powertool battery as one mechanical interface can be used for batteries of several manufacturers. There might be some connections to the power tool other than just a temperature read out that might even stop the charging process, right? The 75/10 apparantly can be adjusted such that the charging and low and high voltage protection will look after a "dumb" battery. I am just at a loss if the battery is too clever...

You must ise the charger that came with the tools. It will have the correct fittings, contacts and controls (including temperature monitoring). It's almost certainly mains powered. So you will need an inverter and suitably sized battery, these things take a reasonable amount of power for fast charging.

Probably not worth trying to rig up a solar powered setup, unless you have all of the kit already.

Nope, not possible.

I use in my little electric tractor and also in the car a Cheap Phoenix Inverter with 250W/375VA which just can power my Bosch GAL1880 Charger without smoking.

It has cost me 130€ and all problems where solved.

Of course, I can not use my Bosch, Makita and FXA Charger parallel, because this would require at least 450W or the Phoenix 800VA version.