[shoesfullofdust]

In my world, AA batteries are all about door locks. There are a lot of card-reading door locks that depend on them.

Whenever a lock fails, step one or two or three is replace the batteries. That's 4-6 batteries per lock.

As a maintenance/security procedure, once every couple of years, every battery in every lock in the entire building is replaced. Doesn't matter if they are dead, weak or brand new. That's hundreds/thousands of batteries.

That's a lot of batteries. And Duracell has multiple levels of "pro"/"industrial grade" batteries. We buy them by the case.

I'm sure the markup on consumer batteries are huge, but I'd also think the commercial use of double-As must dwarf the consumer market. Smart buy by Warren is my guess.

What's needed in this space is a door lock that winds itself much like a "perpetual" watch. Something that takes the mechanical energy used to turn the door handle and turns it into stored energy that can be used to read the card and unbolt the door.

And there you go. Make this thing :)

[btgeekboy]

It already is, though not for hotel room doors/etc. I used to have access to a colo where racks rented individually (i.e. not in a cage) had a combination lock that was electronic. To use it, you first "charged" it by turning the knob back and forth a few times, then entering your code. The correct code mechanically connects the knob to the locking mechanism, so turning the knob unlocked the door.

In the case you mentioned, I do wonder if you could get a bit more energy from the door itself rather than just the handle. For example, if the spring-loaded self-closing mechanisms weren't just mechanical, but used that energy to generate electricity, you might get a bit more out of it.

[lamby]

> To use it, you first "charged" it by turning the knob back and forth a few times, then entering your code.

Reminds me of the telephones where you had to wind them before using them..

[dingaling]

> And Duracell has multiple levels of "pro"/"industrial grade" batteries

What are the differences between those and the retail cells, in your experience?

I've seen people quoting P&G reps that the only difference is the glossiness of the labels and the cardinality of the package, but I haven't found any definitive statement online one way or the other.