There are still rumblings around the web about what should and shouldn't be done with modern batteries. A lot of it is a hang-over from rechargeable NiCad batteries that have 'memory' issues but nobody uses those things now - everything is lithium-ion*. Lithium-ion doesn't have memory issues, but can still be damaged. And the other question is keeping the capacitors healthy.
Agree with Simon - basically just don't let the battery run completely flat, but then most modern lithium batteries will hold a good charge for months. Ideally, store at mid-charge and avoid high temperatures. High temps are best avoided at all times and very high temperatures can cause permanent chemical changes (eg keep ventilated during charging). There's some good advice from Apple re iPhone and MacBook lithium-ion batteries here:
https://www.apple.com/uk/batteries/maximizing-performance/
From a quick google here's another link that says much the same thing:
https://blog.griffintechnology.com/tutorial/what-you-need-to-know-about-lithium-batteries/
Capacitors - the things that actually deliver the (very!) high-voltage dump to the flash tube. I had an old Bowens monolight that had been stored in the loft for about 20 years - plugged it in and it worked like new. But I'm not sure that's the case with modern capacitors that like to be charged and fired a few times.
@Garry Edwards comments would be helpful especially with his knowledge of Lencarta repairs etc.
*rechargeable AA batts like Eneloops are Nickel Metal Hydride (Ni-MH).