I think that Why these two tags have different meaning, they can be merged to include all the questions relating to batteries, which means also battery powered circuits.
What do you think?
I think that, rather than merging these tags into a single, more ambiguous battery tag, we should better define the tags.
With these more detailed tags, it's hard to find a question on which batteries would be more useful. Olin makes the point that it could be used for distinguishing battery technology and circuits which operate on batteries, but that should be obvious from the tag name and it's not if the tag name is batteries.
Accordingly, I've created the battery-chemistry tag. I think this is more meaningful than the alternative battery-technology tag while still being broad enough. (What battery technology questions might we have that wouldn't be fundamentally about the chemistry? If I'm wrong, let me know and I can fix it with a few keystrokes).
There are 223 questions tagged batteries, do 10-20 at a time and this ambiguity will be cleared up quickly. Be careful not to overwhelm the front page with your edits, we don't want the first 5 pages to be all battery questions and the site to become batteries.stackexchange.com until new questions get asked.
Note, too, that if you have 500 rep that you can unilaterally retag a question using the 'retag' button. If you have over 2000 rep (edit privileges), this becomes an 'edit tags' text which appears next to the tags on hover. If you don't have the privileges to retag or edit unilaterally, feel free to suggest these as edits, but please make sure that there are no glaring needs for edits in the question - If you suggest an edit of the tags and the body of the question desperately needs editing too, your edit may be rejected.
No. Don't merge.
Useful as separate entities.
By all means better define them.