Imagine a watch that will run continuously without having to ever be wound… perpetual motion has been the dream since the dawn of watchmaking. Jaeger-LeCoultre has come as close to this as possible with its Atmos clock (pictured on the right is the Atmos Classique), which uses a special gas-filled chamber that expands or contracts due to changes in temperature, winding the clock.

Unfortunately, mechanical watches are still dependent on winding to provide power to the movement to keep it running. In the past, 36-50 hours has been the norm for power reserves – enough for most people, but recently consumers and watchmakers have been demanding more power.

Jaeger-LeCoultre

Power Reserve Explained

The power reserve of a watch is how many hours it can operate, based on the state of wind of the mainspring (a tensed metal coil that transmits energy to the movement). No matter whether the mechanical watch is a hand-wound model or automatic, power reserve is necessary.

If you own only one automatic watch, you don’t really need that much power reserve. You wear your watch all day, keeping it in a full state of wind with the movement of your wrist. When you take it off to sleep and then put it back on in the morning, it’s always running and keeping time. In this case, the lower end power reserve of 36 hours is plenty.

“One of the reasons for the standard power reserve is that extending the reserve has not always been the only priority for a mechanical watch,” says Arnaud Lévy, Head of Research & Development at H. Moser & Cie. “With an automatic movement, for example, an extremely long power reserve makes no sense. The important elements are the habits of the wearer and the type of watch. These factors led to  the minimum seven-day power reserve in H. Moser hand-wound movements and the minimum three-day power reserve (over 72 hours) in our automatic movements.”

Now, people often own and wear more than one watch. That means that the watch that was only taken off for the night is now sitting on a dresser or end table for days or weeks at a time. So, when you come back to wear it again, it has run down and needs to be reset. “The sweet spot for power reserve really is a matter of personal taste and preference and depends a lot on your wearing habits,” says Yann Gamard, President of Glashütte Original. “Those who rotate watches and, therefore, put one aside for a few days, will naturally pay greater attention to the length of the running time.

HMC 100
H Moser & Cie

“With our newly presented Calibre 36, which first beats as the heart of our new Senator Excellence, we followed a rather holistic approach” Gamard continues. “The aim was to create a movement not only beautifully decorated, but also as precise and reliable as possible. It includes a very long running time of over 100 hours at a very stable and accurate rate of performance. With this calibre, we have strengthened our collection, and the extended power reserve was only one of the aspects we looked at in the process.”

With a simple three-hand watch, resetting is no big deal. But if your watch has even a date display, it gets more complicated. Some timepieces, such as perpetual calendars, world timers, ones with moonphase and/or celestial displays and more, often require a watchmaker to reset them perfectly.

The magic number for power reserve really ranges between 70 and 100 hours, depending on your own watch-wearing habits. The minimum should be that you can take your everyday watch off at 5pm on Friday, then put it back on again at 7am on Monday, and it would still be running (this is at least 62 hours). Until recently, there were very few watches that could offer this convenience. Then, things changed.

Glashütte Original
Glashütte Original'
Glashütte Original

Increasing Power Reserve

As watches started to get bigger, and there was more space for bigger mainsprings, options for lengthening power reserve multiplied. As longer power reserves became more in demand, brands started to really work in this area of development, and we are now seeing the fruits of these labours.

Longer power reserve does come with a price, however, either in impact on performance, in size or in price. Think of power reserve as the gas tank of a car: the bigger the gas tank, the greater the car’s range; but the weight is greater, so the car can’t go as fast. The same is true of longer power reserves – you need more space for the bigger barrel housing the longer mainspring, so the watch is bigger, and at the same time, a longer mainspring sacrifices precision.

Calibre 36

So, many companies have included more barrels in the watch to solve the precision issue. “When you use only one barrel, it’s harder to keep the same torque over a period of time,” explains Stéphane Belmont, Jaeger-LeCoultre’s Creative Director. “The watch, on average, will be precise, but the energy coming from the barrel can vary from one day to another. If you have more than one barrel, you have a better linear nature of the power, resulting in a more constant level of energy. A big barrel will take a lot of space, but if you have two or three or four, you can place them so they are using less space in the watch.”

Other manufacturers have used more barrels to solve the power reserve/precision issue. “Our four-barrel movements (Calibres 2253 and 2260) with 14-day power reserves, incorporate sophisticated technical solutions which allow reliability of the movement and stability in the performance, from day one to day 14,” says Christian Selmoni, Vacheron Constantin’s Creative Director. “In addition, they are assembled by senior watchmakers in the ‘complications’ workshop. So, as a result, a great amount of care and watchmaking know-how has been put into such designs, from initial conception to final assembling of  the movement.”

Calibre 2260
Vancheron Constantin
Glashütte Senator Excellence

Hublot’s LaFerrari uses multiple barrels to get to its 50 days of power reserve. “With the MP-05 LaFerrari, we have been working with our teams to reach a reliable 50 days of power reserve, thanks to our manufacture movement with 11 barrels,” says Hublot CEO Ricardo Guadalupe. “If you don’t take the size of the timepiece into consideration, you don’t have any limits in the research of new technologies. For Hublot, the watch has to be pleasant to wear; it is an essential element for us.”

More barrels can lengthen power reserve, but they are also often used to increase precision, as the linked barrels can provide a more constant torque to the gear train. This, however, makes the watch more complex, with more moving parts as well. “Our main calibre has two barrels in order to reach greater precision,” says Taka Hamugushi, Parmigiani Fleurier’s R&D Director, the man in charge of the brand’s Senfine project, which is aiming for 100 days of power reserve.

Hublot's MP-05 LaFerrari

Lowering the frequency, which slows the speed at which the balance wheel turns, has the effect of lengthening power reserve. This can compromise precision, however. When something is gained, often something else is sacrificed.

So, if longer power reserve is the goal, brands have to think outside of the box to solve the problems caused by reaching this goal. An example is Hamilton’s H-10, H-30 and H-40 movements, which offer 80 hours of power reserve. “In the last years, Hamilton invested in R&D not only to develop its own movements, but also to extend the power reserve of its watches,” Sylvain Dolla, CEO of Hamilton Watch, says. “The brand achieved the latter by optimising the barrel wheel and adapting the frequency to 3Hz. These elements enabled Hamilton to extend the power reserve of its movements up to 80 hours. By adding a screw on the balance wheel, we also improved the steadiness of the precision without disturbing the spiral spring.”

Mainsprings last longer if they never go completely out of power. Some watchmakers build in a safety that stops the movement before it runs out of power for just this reason. So, the longer the power reserve, the less likely the watch will completely run out of power, thereby safeguarding the longevity of the mainspring.

Parmigiani Fleurier Senfine

New Materials

Certainly, the materials used in the construction of mainsprings and barrels have changed over the course of time, but the developments  ave only led to incremental increases in power reserve lengths, not leaps and bounds. “New alloys have been developed to improve the storage of energy,” acknowledges Vacheron Constantin’s Selmoni. “We are particularly interested in metallic designs, since they are traditional materials that may be exchanged or repaired in the long run. We still service and repair all  intage Vacheron Constantin watches without exception; by vintage, we mean watches which were even manufactured some 250 years ago.”

Some brands have used silicon and other new materials in the mainspring. “We don’t do the mainsprings ourselves, but I know that  the companies who are fabricating the mainsprings do research and development and come up with more solutions with treatment of the materials, different materials and more,” says Anthony de Haas, A. Lange & Söhne’s Director of Product Development. “It’s not as easy as people think. With a new material, you don’t know what’s going to happen in 10 years, so you have to be careful. We don’t use silicium because we don’t see the advantages and we don’t know what’s going to happen in 20 years. You also don’t know if you’ll be able to reproduce these parts in 50 years.”

Parmigiani Fleurier Senfine

It all really depends on the objectives when a watchmaker develops a new movement and a new watch. “A long or short power reserve depends on the choices you make when you develop a new calibre – its specifications determine the performances you want to optimise, and this, in turn, leads to compromises,” details Pascal Raffy, owner of Bovet. “So, for instance, when you increase the frequency of a regulating organ, you reduce the power reserve. Another example: a small, ultra-thin calibre will be unable to store the energy required for a large power reserve.

“As far as Bovet is concerned, our experience in long power reserves goes back as far as our history,” Raffy continues. “Many pocket watches manufactured in the 19th century already offered eight days of power reserve. Since the early 20th century, Bovet has held an outright record for a pocket watch (part of the collection displayed at the International Museum of Horology in La Chaux-de-Fonds) with 370 days of power reserve. In any case, all the movements we produce today have a power reserve of between five and 22 days.”

Bovet 1822's Braveheart Tourbillon

Everything is a compromise – if you develop a new system that requires more energy to operate, power reserve can suffer. “If you take the Zeitwerk, for example, it was a huge challenge to get more than 36 hours, because we use discs to display the time and they are quite heavy and need a great deal of power to move them,” says Lange’s de Haas. “You can always make the barrel bigger. But if you just make the mainspring bigger, it’s not one to one. It’s a nasty calculation. That’s why we used the remontoir spring system that recharges every 10 seconds. If we went to 20 seconds, we would have to make the remontoir spring stronger, then we would have to make the mainspring stronger.

“With the Lange 31, we had hands and an oversize date to move every 24 hours, and we had two extremely long mainsprings (1.85m). We were the first with 31 days, and this development taught us a lot. When we were doing the Lange 31, we found the solution for the Zeitwerk. By putting the remontoir system into the Terraluna for 14 days, we learned how to do the jumping second. During the 31 days of the Lange 31, the remontoir system has the same accuracy on day one as day 31.”

A. Lange & Söhne Zeitwerk

The New Normal

Most brands agree that lengthening power reserve to a more reasonable 62 – 100 hours is the wave of the future. As more and more watchmakers focus on longer power reserve, the market should see many more options. And, the higher end solutions on the market now should trickle down to entry-level watches.

This is important for the first-time buyer of a fine mechanical timepiece, as they may not be aware of the need to keep their watches wound. “More and more watches are 72 hours,” says Lange’s de Haas. “For us, it’s the same, if the watch can handle it, technically speaking, then you can do it. We are not willing to make big compromises – it must not have an influence on the timekeeping, and we need to have a certain amplitude on the balance.”

The Outliers

Take a look at the photo gallery on the Battle of the Power Reserves Commences, of the industry’s longest power reserve watches and you’ll be amazed at the lengths some brands have gone for power reserve. These kinds of developments are necessary for the industry, in general, to move forward with longer power reserves.

Remember the Atmos clock from the start of the article? “Many people have tried to take temperature changes and create energy, but keep in mind the frequency of the Atmos clock is very low (it makes one back and forth in one minute), so you save a lot of energy,” explains Jaeger-LeCoultre’s Belmont when asked about adapting that technology into a wristwatch.

“Nonetheless, you can see how big the container with the gas is in the Atmos clock, so if you translate it into a watch, the gas capsule has to be 240 times bigger than the watch, so you would have to carry it in a backpack. The automatic movement is already a perpetual movement as long as you wear the watch.”

Jaeger-LeCoultre

HYT, which pioneered the use of liquid in the time display of their watches, is doing research on a system that takes temperature variation into consideration. “We are developing a system which can capture the temperature changes of your body (the watch being on your wrist),” says Vincent Perriard, president, HYT. “As you know, we are using bellows in our technology. So if you have temperature changes, the bellows, which are filled with liquids, will retract or expand. So we are working to create a movement where we will be able to capture temperature changes (even very small ones) and turn this into energy. After the mechanical, manual winding, the automatic movement (with oscillating mass), the quartz watch, we will come with a Fluid Power device.”

You can expect the power reserve of watches to evolve, especially now that brands and consumers are paying attention.

HYT's H2 Tourbillon

“Watchmakers have always strived to be the best, particularly during the 20th century,” says Bovet’s Raffy. “The thinnest watch, the most complicated watch, the most expensive watch, and so on. The question is, do we want to rack up records or offer reliable technical solutions that meet the needs and requirements of today’s collectors?

“The complexity of the power reserve/frequency/chronometry compromise led us to carry out a great deal of research on this issue,” he continues. “Our development team has obtained some crucial results that have enabled us to file various patents over the past few years. These include the spherical winding system and its tridimensional toothing with multiple gearing, which are patented and present in our Braveheart tourbillon (22 days of power reserve) and, more recently, in our Ottantasei tourbillon (10 days of power reserve).”

Pininfarina OttantaSei

Where Will It End?

When watchmakers create a new watch, power reserve is only one of the things that they take into account. There is the design, the functions, the precision, the size and more to think about.

Personally, I think that it makes sense for entry-level watches to offer at least 70 hours of power reserve, so that the owner isn’t resetting their watch all the time. Watches with more displays (day, month, year, moonphase, etc.) should have longer power reserves because there is more to reset if the watch winds down.

Sure, it’s fun to think about watches with 31, 50 or 100 days of power reserve, but these are wonderful exercises and showcases for technical developments, but do we really need watches like this?

“If you have a watch that is so boring you don’t want to wear it and you need 100 days power reserve, it might not be the best watch for you,” points out Jaeger-LeCoultre’s Belmont.

For regular line watches, however, if more consumers demand better power reserve, watch companies will answer the call and provide longer usable power reserves. The bottom line is that if we all ask for it, we’ll get it.

And we deserve it. Power to the people!

HYT's H2 Tourbillon

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