Power Reserve

Power reserve is the length of time a watch will keep running, fully wound, if it is simply left untouched. It is measured in hours and set by the mainspring and barrel design: most modern automatic watches offer somewhere between about 38 and 80 hours, while a smaller number of movements — built expressly for the purpose — run for five days or more.

Why reserves differ so much

A mainspring stores a finite amount of energy, and the movement spends it at a fixed rate. Longer reserves come from longer springs, larger or multiple barrels, or movements geared to sip rather than spend. There is a trade: the long-reserve calibres that run a week are engineered showpieces, while the everyday 40-hour movement accepts that its owner wears — or winds — the watch most days. Reserve figures are also quoted for a fully wound spring; a watch that spent the day on a desk has taken in less and will stop sooner than the headline number suggests.

Power reserve is why two owners can have opposite experiences of the same habit. Leave a 38-hour watch unworn over a long weekend and it stops. Leave an 80-hour watch and it is still running on Tuesday. Neither watch is faulty; they simply carry different amounts of time with them.

Some watches show the figure rather than making you remember it: a power-reserve indicator — a small hand and arc on the dial, sometimes labelled réserve de marche — reads the spring's remaining charge like a fuel gauge. It is one of the genuinely useful complications, and the one winder owners consult most: a glance tells you whether the watch went onto the winder full, part-wound, or barely alive.

What it means for your winder

Power reserve decides how urgent a winder is for any given watch. A short-reserve watch in a rotation of three or four pieces will stop between wears without one; a long-reserve daily wearer may never need one at all. Reserve also shapes settings expectations: a winder's job is to maintain the state of wind, replacing what the movement spent during the day at its required turns per day. It is not a fast charger. A watch that has run completely flat is best brought back with a careful hand-wind where the movement permits it, then kept at level by the winder. You can check any model's settings in our TPD database before deciding whether it belongs on a winder or in a box.

Frequently asked questions

Does a longer power reserve make a watch better?

Not inherently. It makes it more forgiving of being left unworn. Accuracy, finishing and reliability are separate questions; reserve is convenience, measured in hours.

Does using a winder increase my watch's power reserve?

No. The reserve is a fixed property of the movement. A winder keeps the spring near the top of that fixed capacity, so you always have the full reserve available when you take the watch off the winder.

My watch stops overnight even though I wear it daily. Is the reserve failing?

Possibly it is simply under-wound: a sedentary day may not fully wind an automatic. Try an active day or a gentle hand-wind first. If a fully wound watch still stops far short of its rated reserve, the movement likely needs a watchmaker, not a winder.