Battery Design Changes?

Factual Questions
1

Not long ago, one of the smoke detectors in my house started chirping intermittently, signifying that it needed a new battery. I bought a fresh 9 Volt, slid out the battery tray, and popped out the old one.

The tray in question is only a bit wider than the battery itself, mostly open to the bottom so one can look up into it, with the contact portion closed to the bottom to support that end of the battery. The other end of the tray has two plastic ridges running from top to bottom to hold the base of the 9 Volt up and press it against the contacts.

When I put in the new battery, it wouldn’t stay put; rather, it just fell out! I tried putting it in, then holding it in place as I slid the tray shut, but the chirping persisted. I reinstalled the old one, and sure enough, it snapped right into place. Comparing the two batteries, I noticed that the old one had a thick, rolled edge around the bottom that locked into a notch in the retaining ridges, while the new one’s base had only a small, thin flange of metal holding the bottom on, not thick enough to snap into place. Using a very thin screwdriver and a pair of needle nose pliers, I pried up a little of the flange on one side of the new battery, approximating the rolled edge of the old one. Sure enough, it snapped into place and held without complaint, and the chirping stopped.

What I’m curious to know is why did the design of 9-volts change, does anyone still make them in the older style, and should I buy new smoke detectors rather than modify future batteries?

2

I don’t think the actual specification (ANSI 1604A) says anything about the construction of the edges, just the overall size of the cell. Here’s a data sheet (WARNING - PDF):

http://www.moltech.com/pdf/Moltech%20Professional%209V%20Data%20Sheet%20Issue%202%20June2005.pdf

Possibly, the detector manufacturer was taking advantage of a construction technique that was common practice, but not actually enforced by the standard.

3

I see what you mean about the construction; that document doesn’t say much at all about the exterior, save dimensions and material (and “metal” leaves plenty of leeway in that department). I did notice the other day a rechargeable 9v that has what looks like a plastic housing with very rounded bottom corners. I imagine that might cause some issues if a device design took a boxier battery for granted.

4

Note that the pdf isn’t actually the standard, just a manufacturer’s spec sheet drawn from it, particularly the dimensions. Before somebody comes along to nitpick, I know that the 9V battery isn’t actually a “cell” - it typically contains 6 1.5 volt cells. The data sheet makes this same mistake, too.

5

One of my pet peeves is that 9v lithium batteries are just slightly too big to fit into any normal 9v battery holder.:mad: