My daughters wants a smart watch that can connect to the internet for Messenger, Line calls. The 4g ones are the only ones I've seen with internet connection but the battery life isn't so good. If she doesn't insert a SIM card  keeps it on airplane mode and uses only WiFi connection will it improve the battery life much.

Thanks for any help forthcoming.

I’ve got an Apple Watch that has the capability of connecting to the Internet via a

its own separate phone line, but I’ve never used it that way because it syncs up with my phone and I always have my phone with me. The watch will still get messages and email, and you can answer phone calls right from the watch.  Anyway the watch’s battery seems to last two days before it runs out. Usually, though, I charge it every day, as it charges pretty quickly.