Keeping the battery topped up is only healthy for old lead technology.
With LI, just disconnect it so nothing runs it down, it is unhealthy for longevity for it to be kept Full.
Really long term storage, drop its voltage down to 30-40% SoC or 3.7 - 3.8Vpc, precision is not required.
But check it enough to be **sure** you don't let it go dead flat either, can render it scrap very easily.
