David Hanak As this year's September novelties gradually reach their new owners, there is also a series of various tests that accompany each new model launch. One of the more popular ones is a complete analysis of new products from iFixit, thanks to which we will learn mostly the latest specifications that Apple managed to keep secret (whether on purpose or not). Probably the biggest surprise so far is the new battery in the 40mm variant of the Apple Watch Series 5.
Although Apple did not talk about any more specific changes with regard to the batteries, and practically nothing has changed in the 44mm model, the dissection of the 40mm model revealed that it contains a completely new type of battery, which is both structurally different from its predecessors and also has a higher endurance.
A thorough analysis by iFixit showed that the battery in the 40mm variant of the Series 5 has a completely new case, which is probably made of aluminum, and is slightly more compact than the previous design, so it can fit a larger battery. Inside the packaging, there are actually battery cells that have 10% more capacity than the same battery module from last year's model.
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The new outer casing of the battery should also be much more durable than it has been so far. This should make the battery more mechanically resistant, which should, among other things, prevent it from swelling. This has happened to some Apple Watches in recent years, and Apple has had to replace damaged watches. So Apple seems to have killed two birds with one stone with this solution.
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Petr Škuta 
It's interesting that it does this with a smaller model, which, in my estimation, is sold much less.