I’ve been using Tailscale for about 2 months now. It has a VPN-on-demand setting that I keep enabled. That way, anytime I am not on my local WiFi, it automatically connects the VPN. According to my battery health settings, Tailscale has used 5% of my battery in the last 10 days. And I am even using a Mullvad exit node, which would use even more battery.