Upgrading to 16GB won't noticeably hurt battery life.

Not in any meaningful way.

Yes, more RAM draws a tiny bit more power—think maybe an extra watt at most. In a laptop that pulls 15-30 watts under normal use, that’s a few minutes off a full charge. You won’t feel it.

What actually kills battery is having too little RAM. If you’re constantly swapping to disk because you’re running out of memory, the SSD and CPU work harder, which uses more power. Upgrading to 16GB can actually improve battery life if you were hitting that wall.

Bottom line: buy the 16GB. The power difference is noise.