While 18 hours is what apple says, their scenario for 18 hour usage is probably very uncommon.
At least for me it is. And thus I get around 2 days battery life with a 4 year old series 2 watch.
Their official test includes "45 minutes of app use, and a 60-minute workout with music playback from Apple Watch via Bluetooth"[0] - so unless you plan on doing that you can easily expect double the battery time.
It does feel really good to go on a jog without bringing my phone. That’s my favorite part of my Apple Watch, upgrading from the series 0 to the Series 6 cellular. I barely wore my series 0 and got bored of it, but the 6 feels indispensable.
At least for me it is. And thus I get around 2 days battery life with a 4 year old series 2 watch.
Their official test includes "45 minutes of app use, and a 60-minute workout with music playback from Apple Watch via Bluetooth"[0] - so unless you plan on doing that you can easily expect double the battery time.
[0] - https://www.apple.com/watch/battery/