A watch’s power reserve can be an overlooked function when buying a watch, but it’s important if you wear multiple watches. When a watch’s power reserve runs down, the watch stops keeping time, and you need to reset it. If it’s a simple time-only watch, it’s not much of a hassle, but if you have a complicated watch, like a perpetual calendar or a moon phase, it can be time-consuming to reset the different functions, so having a watch with an ultra-long power reserve is beneficial. While some of these watches have incredibly long power reserves — Vacheron Constantin currently holds the record with 65 days — a good rule of thumb is the so-called weekend test. If a watch has a power reserve longer than 62 hours, you can take it off on Friday night after work and put it on again on Monday morning, and it will still be running. Read on to discover the watches with the longest power reserves.