Solar charge 36V bosch type garden tool batteries

Hi guys
two things:
1.Anyone know of a solar charger for these batteries.Or ever tried to make one: Seems the dificulty is on choosing the right MTTP charge controller and preventing discharge below 40% Anyone tried ?
2. Portable outdoor higher amp hour supply for these tools: I am building one also solar charged Lithium. Plan strip existing 36V battery: Just leave the casing Put a plug/socket into it: Remove battery when it runs low Slot in modified casing and Connect by cable to portable dc outlet.
Then I can keep going.
Has anyone got a knackered bosch 36V battery pack I can strip ?

PS I dont care how long it takes 1-3 weeks to charge from my solar array. Doesnt matter Grass doesnt grow that quick ! So I can have a very small array on my shed roof. ( in the UK little sun anyway)