cats

A normal AA battery is probably more powerful than this tiny thing. That cell is probably 3.7v 250 mah at best. My “shitty” ikea rechargeable AAs are like 900 mah, and the good ones are 2400 at 1.2V. 3.7 * 250 is 925 watt hours, 1.2* 900 is 1000, and 1.2 * 2400 is 2800.

The biggest benefit is these are easily and quickly rechargeable.

By "regular" batteries I assume you mean alkaline ones like your standard AA and AAA. Lithium Ion batteries aren't really more "powerful", more likely the circuit was simply designed for constant 5V because that is cheap and easy nowadays. Small lithium batteries like the one used here and a simple charging circuit and port are dirt cheap when purchased in bulk.

Not to mention there's a size difference both for the battery itself and mounting area for it. For something like a AA battery there needs to be a user accessible battery compartment to replace them. It's cheaper and easier to just not do that.

It's a fairly common type of cat toy...

I updated the post to reflect the "(cat)" toy nature in the alt text first line. Sorry I took this for granted as a clearly understood context as a common cat toy (in the USA) and failed to describe it as such.

I posted it here because I wanted to reach the most significant audience. Posting this in electrical engineering would have missed the majority of people this is intended to inform.

You're getting down voted but I was wondering the same. I had no idea this was a cat toy.

maybe it's a catfish