This is something I noticed yesterday, bought a new 9V battery for my DMM, and then I had the idea to measure voltage of the old battery.

It is still 6.5V, good to use for many purposes.

So if 9V circuits/devices don't work anymore, and you replace the battery, check the voltage. It still might be good for some purposes.

 

But realize that, at 6.5V, which is slightly over 1V per cell, there is very little energy left in the battery.

 

This is something I noticed yesterday, bought a new 9V battery for my DMM, and then I had the idea to measure voltage of the old battery.

It is still 6.5V, good to use for many purposes.

So if 9V circuits/devices don't work anymore, and you replace the battery, check the voltage. It still might be good for some purposes.

For alkaline, 1.5V is what's generally appear on a fresh battery. At 1.08V average, you are looking at a very small percent of remaining capacity (>5% I believe) at a very high voltage dropping rate when used. It's not worth it to salvage it. You can use it as a voltage reference that almost draw 0 current, and that's about all I can think of for application.

 

And all along I thought 9V batteries were only just for "tongue ticklers"

 

Use it as LED tester! I tried and indeed the battery does not have capability to damage the LED.

Powering a PIC 18f24j10 + 2 LCDs does not work, however. The LED blinks a little just at the margin but then goes out.
The charge pump ICs on the LCDs don't seem to be very efficient...

Normally this should work since LCDs only need 1mA or the like.

I will put it next the 4.5V battery on my desk

They are both good for destruction-free component testing. If I want to destroy component, I use 2kW welding transformer- 60VAC.

Seriosly- I have tested IR receiver with 4.5V battery + wires, as pinout was unknown. It survived wrong connection- the battery can not provide enough currents for destruction.

 

When my batteries time is 'up', I put them in the bad battery drawer and occasionally visit the household hazardous waste facility in San Pedro and give them a bunch of batteries to find a new home for.. The remaining rechargeable batteries get recharged and put back into service.. My kids go through craploads of batteries! I've vowed to not buy anymore batteries --instead buying rechargeable types only -- Amazon has some great prices for them too -- for their house brand.