Earlier quoted context omitted.
For my use case, it's quite obvious what's draining the battery: addons. Every trick and feature meant to preserve privacy and to remove visual trash will significantly impact load times, responsiveness, and battery life. It's all worth it to me, but there's no doubt a web without tracking and ads would easily double my battery life.
It seems obvious to me that uBlock Origin uses less battery than an autoplaying video in the corner of every website you visit. So on balance I don't think it's fair to say the addons are the cause.
That said, it's been ages since I've last seen an autoplaying video. I only seem to encounter them on American news websites for some reason.