Blokada is a VPN based adblocker, but Adaway can work as a hosts file based blocker, if the phone is rooted. Hosts file based blocking uses zero cpu cycles, as it’s a feature of the network stack, it’s just a file containing list of addresses to redirect, so it should use less battery than blokada. By default on all OSes this hosts file is not editable by regular users, that’s why you need root. Wikipedia article about hosts file