Your Apple Pencil's battery should last for many hours of active use. Given that (a) the Pencil will rapidly recharge when docked with the host iPad - and (b) it is generally recommended that the Pencil is docked with the iPad whenever it is not being actively used - battery longevity between charging events is generally not an issue.
Keeping the Pencil docked with the iPad when unused ensures that the tiny internal battery is kept optimally charged when not in use. Charging only occur when the battery requires charge from the iPad, optimal charge being entirely automatic.
Keeping the Pencil separated from the iPad when unused risks allowing its battery to discharge; if allowed to remain in this state, the battery will suffer irreparable damage. When the battery fails, the only remedy is to replace the entire Pencil; the battery is not a serviceable item.
An otherwise healthy Apple Pencil will suffer no negative consequences from being docked with its host iPad for extended periods.
Charge your Apple Pencil and check the battery - Apple Support