Does a device exist where one can use AAA batteries in AA slots?

Not in the way you are describing.

There are several battery chargers – Energizer makes some, Samsung does too, wherein the same slot will charge an AA and an AAA – but not at the same time. They built the charger to accept both sizes of battery.

I own this one link

As far as fitting in other devices like remote controls – I suppose it is theoretically possibly do build it, but I have never seen one for sale.

I’ve NEVER tried it because I’m afraid of what might happen; however, I’ve read that you can put a AAA battery in place of a AA. You just lay the AAA in the same slot & then take a piece of aluminum foil & fold it over to place between the battery post & the connector. This is NOT supposed to be a permanent replacement…just a temporary fix!!!

Yes. Look for AAA to AA battery adapter

They are both 1.5 volts, so the AAAs work the same in a device for a shorter time. The size gives you an idea how much shorter.

@Call_Me_Jay What about an expandable battery then? Has that been invented?

@Call_Me_Jay I did a quick Google search and found a expandable battery. It exists.

@Call_Me_Jay THANK YOU for the info!!! I popped over to Amazon & did my trusty search. As I said, I was too scared to try the aluminum foil, but probably would have when in a pinch. I bought the adapter so I can keep one in my purse for when needed & the spare in my battery drawer at home. Most items I use that need AA batteries are few & far between & I use a ton of AAA’s.Even the adapter is made for temporary use; but, I think would be handy until I could get to the store. The description does warn that the AAA won’t last as long as the AA battery would. I feel safer with the adapter. Using the foil made me feel like whatever I was using it in might burst into flames while in my hand!!! My adapter will arrive on Wednesday & I can update @RedDeerGuy1 on its usefulness before he buys one.