I mean, for a phone yeah, but a small, relatively cheap waterproof device with a battery under a watt will probably start having issues at 5 years, more likely much before that. Waterproofing something that small will probably not be easy after replacing the battery, so while you probably will be able to eventually, it probably will be a little more fragile afterwards. I’ve got a fitbit, and I’ve seen the videos of replacing the 0.25 watt battery, would for sure doubt it’s water resistance afterwards, probably easier to replace.