I got Mullvad VPN to try it for a month after years using ExpressVPN, but it drains my battery (iPhone SE, 2nd generation, 2020) into oblivion in a matter of 3-4 hours.
Browsed the Cursed Site™️ and using WireGuard instead of the Mullvad VPN app seems to be the most common solution – but not for me. WireGuard either it doesn’t connect to any location or disconnects after 2-3 minutes.
Anyone got any advice?
EDIT: added more details about the phone model.
You also might try changing VPN protocols. OpenVPN and Wireguard are the 2 most popular, and there’s also L2TP on certain providers. For me OpenVPN drains faster than Wireguard. And if I remember correctly, using L2TP on Mozilla vpn drained like 0 battery when I tried it, although L2TP is developed by Microsoft so take that into consideration