500 lb. koolaid man

Just as the title says. Can you use a multimeter to find out the mah of a battery? If not, is there a way? Thanks.

Straick

Not that I know of. The way I've done it is to fully charge the battery in question, and then discharge it with my charger, which will then readout the MAH of the batt.

Access

You need a multimeter, a constant current load, and a stopwatch, and then you could do it. You could in theory do it with a normal resistive load but then it's a calculus (area under the curve) problem and the math is beyond most people.

SAVAGEJIM

Ah! Integral calculus! Surprisingly, calculus is not that hard at all, and most highschools now require it as part of high school (and even late middle school) course work.

What kids are learning today is leaps and bounds of what highschool used to teach even 10 yrs ago. Has anyone even seen what a 5th grader has to learn? Stuff that highschooler of 10yrs ago didnt even touch until they were juniors or seniors!

500 lb. koolaid man

I'll skip the calculus option

So I have the battery under a load with the multimeter on it set at 200ma which is the best setting for it... and the clock keeps track of drain time or what. I'm confused so please elaborate. Thanks.

Straick

If you have a load of X amps, and your time to your cutoff voltage is Y, then you just multiply them together to get your amp/hour rating. Multiply that by 1000 to get your milliamp rating.
Example:
You have the battery giving a current of .5 amps.
It takes 3 hours to get to your voltage stop point.
Multiply 3X.5 to give you an amphour rating of 1.5, or 1500 milliamp hour.

Access

The problem there is you need to build a constant-current load (one that does not vary with voltage). A resistive load varies greatly with voltage, ie. a 1-ohm resistor will draw 1.2A at 1.2V and by the time the battery drops to 0.9V, it will only be drawing 0.9V. You can kinda fudge things by taking the average, but you're going to lose real accuracy if you do that.

Straick

I've done this before, and never want to do it again. I used 2 mutlimeters. One was reading the amp draw, and the other the voltage. For my load, I used a variable resistor, and as the voltage dropped, I adjusted the resistance to keep the amp draw the same. A lot of work, and you have to babysit the batteries. Not easy or enjoyable. Much easier and simpler(and more accurate) to just get a charger/discharger that reads out the capacity of the pack.