One of the complaints people often have about Sony’s E-mount cameras is their battery life. They don’t get the life most SLRs get. Sony could fit bigger batteries, but then the cameras would be bigger and heavier, and one of the reasons for choosing these cameras is having less to carry. It’s the reason I switched over years ago.
The thing is, I get much better battery life than you’d expect. On my last trip, I took over 500 photos, and still had over 40% of the battery left. I think the difference is that I only use manual focus ‘legacy’ lenses – either vintage ones, or modern Leica-mount lenses. Quite a bit of the power use in a modern camera is the lens. They use power for focusing, and for extra features like image stabilising. They’re pretty much a little computer with a bit of glass to move around, and it all uses power.
Stick a manual lens on the front, and the camera doesn’t have anything to power but itself. That’s still a hefty power draw, with the sensor and screen(s), along with image processing, but it’s less than there would be with the lens too.
So, switch to manual lenses for better battery life? I wouldn’t go that far. If you don’t want to use them for other reasons, I’d just take an extra battery, but it’s a nice bonus if you like working that way.