I did a 5 battery a few months ago, in about 25mins. Had I been sober enough to see anything, would have been 10-15 mins less
With my eyesight hope for me then when my iPhone 5s battery needs replacing.
Last weekend it was almost flat on standby in about 36 hours.
Having said that I soaked my normal watch, on Saturday, which stopped working and my smart watch a stainless steel Casio Databank battery was flat and I had every type except a CR2016.
Ordered two through the post which turned up on Tuesday, checked my normal watch where I had left it drying out and still not working. Took the back off the smart watch and the battery clip was a pig to unclip and when it finally did ping there are 4 very fine springs, 2 which are used for a back open switch which were still in place and 2 for the case back alarm bleeper contact which had gone walkies.
These spring are about 3mm long and 0.75mm in diameter and are on the floor somewhere.
After about 10 minutes of scanning the floor with a torch and magnifying glass I found one of them and about 5 minutes later the other one.
With a new battery watch was working outside of the case and each time I held it together okay, but once I replaced the back using a bright torch and magnifying glass to see where the fiddly 2x0.5mm screws locate and doing them up to hold the back all it displayed was a 0 with nothing else working including the buttons. By trial and error finally got it working where making sure the case cas located exactly right and the order of tightening the back screws made a difference.
Went to sling the broken watch in a draw and it was working perfectly. Sods law at its finest.
But at least my scratched up plastic cased everyday watch will carry on getting further scratched while the smart one stays smart where I will only use it when I go out now it is working again.