Leaving NiMH and LI-ION powered devices (toothbrush) at charging station
For the NiMh one I would not leave it charging all the time. Although NiMh cells do not have much "memory effect" in my experience they last longer if you do not charge them after every use. I would use them until you start noticing they're running empty or you think they will be empty soon. You don't have to run then completely down to where the device stops working though (that was only needed with the old NiCd cells).

For the Li-Ion one you can recharge it after every use if you like, these cells do not mind being recharged all the time. The charging circuit will stop charging the cell when it's full anyway.

But if you would apply the strategy of the NiMh (dicharge until almost empty) to the Li-Ion it would also last a long time. I have a (Philips) shaver with a Li-Ion cell and I only charge it when it is almost empty (the shaver has a display so I can see when it's almost empty). It is lasting for more than 5 years already ! OK, I notice that the cell is wearing out a bit but I can still shave for weeks after a charge.