All batteries have a tendency to self discharge and that tendency will get worse with age. However good batteries do will not self discharge as much as cheap ones and they will live longer. I personally have Canon gear and have bought both "no name" batteries
and Canon brand batteries ... my experience has been that the Canon brand ones live much longer than the "no name" ones. I have Canon batteries that are well over 5 years old that still work fine. Many of the "no name" ones gave up the ghost in a year or
so.
Bottom line recommendation ... buy good batteries and keep them charged [if you don't use them for a few months]. In the battery world you definitely get what you pay for. This is in general for the current Li-Ion batteries. But se sure to watch for any
signs of leakage ... if you see that toss the battery immediately before the camera gets [expensively] damaged...