Not sure is it same, I don't use tailscale, but using pure wireguard. In my experience battery drain is not even noticable, but staying connected is not smooth as I'd like. I tried to keep active VPN all the time, but then sometimes I just notice my internet is not working ( I have disable or restart VPN connection). It could be issue with my phone (Android), missconfig or something else, but I switched to manually enabling VPN every time I need it. Not amazing, but few clicks every now and then is more than acceptable for my use case