If he changed the circuit to “make end multiplication unnecessary”, he’d likely be losing accuracy, as all of the sudden a change in the amount of amp/hours would correspond to much smaller amount of change…

Or he could just change the numbers on the face of the clock…

a deep discharge protection should be implemented or it might be the last cycle of the battery ;)

I would use an arduino to do the math and then have it twitter the test results from each battery. c’mon hackaday, get on the ball!

@pdx: A little of both. Yes, you can go through a resistor, but this way you can reliably time the discharge with a given current draw. Otherwise, you’d have to sit there and watch your meter the whole time, noting down when the battery died.

;)

Wtf….. I just use a capacitor and a poteniohmer to calculate the end of the universe for my lipo’s

Hmmm.. I have a watch EXCCTLY like that one and it is all analogue, no batteries inside, only an old school proper wind-up mechanism.

It would be simple to measure the time with any other device, but the circuit itself is simplicity at it’s best. Though if the “true” mAh rating is what you are after I don’t think you are going to get it with this since the “true” rating is usually done at a 1/5 C discharge rate. By “true” I mean what the factory puts on the label… you know, marketing crap.

@till: a pseudo deep-discharge is already in place: the white led. Of course you will still have leakage current through the PNP transistor, but that should be negligible unless you leave this thing hooked up for weeks.

As for making the calculation unnecessary, make it draw 1mA (yes, impossible with this circuit). Then see the number of hours it runs. :D You could make it easier though: change the total resistance (including parallel relay coil) to about 37.5ohms (drawing 100mA) or 3.7ohms (drawing 1A). A 1A draw should be well within the 1C discharge limit of most LiION laptop cells and give more of a “real world” capacity, just make sure your resistor(s) can dissipate that kind of power.