For example, while the original battery capacity for Apple Watch Series 1 (38 mm) is 205 mAh, can I replace it with a 273 mAh (38 mm) battery (originally for Apple Watch Series 2, 38 mm), and assuming if it work, would extend the standby time for Apple Watch Series 1 (38 mm) much longer than the original design? Will it work, and be safe?

  • If you have your AppleCare+ warranty on the watch, I'd recommend not doing it. Also by opening the watch, keep in mind that the screen is very fragile and with crack if not handled exceptionally careful. – Melvin Jefferson Aug 18 '18 at 23:05
  • @melvin-jefferson Thanks for the advice! Yea but when warranty expired, and the the screen lifted because of the battery, I guess what can be done is replacing the battery --- that's when I start to think, since the battery will be replaced anyway, what if replace one with more capacity, will it get longer standby time? --- that's why I'd like to know, in the first place, can I change the larger capacity battery and will it be compatible? – Bill Aug 19 '18 at 0:02

Changing any lithium ion battery that isn’t enclosed in protective metal is unsafe. If the part is crimped or pinched or you get a screw loose, the consequence is fire. Just like a home repair of a gas line or working on live electricity isn’t safe in general. It doesn’t mean some people can’t do it, but that most people shouldn’t without some education and training and the willingness to start over if they mess up with one part.

Apple gear is so small and light that the internals can be tricky to repair so I’d take it to someone that does dozens of these swaps a week or more if you concern is about safe.

  • Thanks for your advice! You are right, and I was hoping to see if there is this expert "someone" here could tell me: Above all, if a 273 mAh battery from Apple Watch Series 2 could be placed in Apple Watch Series 1, whose original battery is 205 mAh? will it be compatible? And then, if it works, will it be safe? – Bill Aug 19 '18 at 0:08
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    @Bill Go ahead and ask a follow on question. What physically firsts is a great question. I know a lot about safe but not about parts. Someone who knows that would be a great answer. Especially if ifixit.com or some other source hasn’t documented the details of a battery swap on a watch. You’ll need to know all the parts and tools and steps in addition to the yes/no part about fit and operation. – bmike Aug 19 '18 at 1:31

It turned out that the battery of difference series of Apple Watch is not compatible with each other, due to their connector interfaces are very different. [reference] So, as much as safety has to be concerned, the idea won't work in the first place.

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