12C battery life: 3xLR44 model vs. 1xCR2032 model

[BobVA]

Well, the energy capacity is about the same for LR44 and the 2032 (150 x 4.5 = 675 mWH vs. 220 x 3= 660 mWH) so, theoretically, they should have a similar lifetime about if the power requirements of the two models are similar.

I wasn't sure of that assumption, so I did some quick measurements on my 12c Platinum (single 2032 but unknown variant) and a regular 12c and got the following results

Code:

                On                      Off
    12c     67.1 uA (0.3 mW)       <0.1 uA   (<0.45 uW)
    12P     29.6 uA (0.1 mW)        1.5 uA    (4.5 uW)

I didn't measure current for processing keystrokes, running programs, etc. figuring the average calculator spent the majority of its time in the off state, and the idle state after that.

So, based on all that, I'd expect the batteries in the 12c to last longer due to it's much lower "off" power consumption.

And here's some the reasons that could be wrong, or right for the wrong reasons:
- measurement of current that low with a simple DVM is fraught with peril (but I think the relative measurements are perhaps more reliable).
- I couldn't get a reading on the 12c standby current as it dropped below 0 on my meter after a few seconds. I was guessing it was closer to 0.1 uA than, say, 0.01 uA, but I don't know.
- I don't know exactly where the Low Battery warning is tripped on either model, nor the energy under discharge curve for either battery type when reaching that point. Both silver oxide and lithium batteries are relatively flat, so the latter *may* be a wash.
- There are a large number of variants of the single 2032 12 Platinum and I don't know if I have the one you're asking about.

But, the most important thing about this experiment is I discovered a set of leaky batteries in my 12c! :-)

I also discovered a little piece of paper in the 12c battery compartment on which the previous owner had noted the battery change dates. They seem to bear out the Voyager reputation for battery life:

- December 22, 1993
- June 1, 2005

I added today's date to the paper and put it back in the battery compartment to keep his or her experiment going.