No. One night at full costs a lithium cell almost nothing, and the charger stops when the cell does — the habit only matters if the tool also spends the night somewhere warm.
A trimmer charges in one to two hours. Leaving it connected for eight means roughly six of those hours are spent doing nothing at all, because a lithium circuit tapers and stops rather than holding the cell under current.
What is left is a small, slow effect: a cell sitting at 100% ages faster than one sitting at half, and warmth multiplies that. So if the habit is worth adjusting at all, the thing to adjust is where rather than whether — a radiator shelf or a steamy bathroom is a worse overnight spot than a bedside table, and that matters more than the hours.
Against that, consider what charging overnight prevents: a flat tool halfway through a trim, which is the failure that actually happens. On a tool with no quick charge — and only five products here publish one — a flat battery is the end of the session.
Two things that are worth avoiding, both documented rather than inferred: leaving a tool flat for months, and charging a cell that has been somewhere below freezing before it warms up. Cold is the one that does lasting damage.
For the broader version of this question — a tool that lives permanently on a stand rather than one night at a time — see leaving a tool on charge.
Check your own manual before you follow anything here. Temperatures, water ratings and supply voltages differ from model to model, and the maker’s own figures take precedence over anything written on this site. A supply of the wrong voltage is a failure rather than a slow charge, and the figure is printed on the tool — not inferred from a connector that happens to fit.
Last reviewed October 10, 2026