Testing Battery Amperage

[Chakthi]

I didn't know where to post this question, so I hope it's okay to put it here. I have some questions about something I just read.

This guy in another forum was asking if he could test the amperage of a battery with his multimeter. There were many various answers, but there were two in particular that caught my attention, and I'd like to know what the correct answer is.

One guy told him that if he put the probes of his multimeter on each end of the battery with the meter set to measure amperage it would give him the battery's max discharge - that the battery would put out as much current as it is capable of.

Another guy though said that the only way to measure the current from a battery is if the battery is under load - that you have to put the meter "in series" with the rest of the circuit. I assume that means, for instance, putting the probes on the positive end of a flashlight and the negative end as well, and turning it on?

Which one is correct? Is it even possible to determine the max discharge of battery with a multimeter? Idk.

This also made me wonder about something else that's related. When we put our batteries in the charger to charge, we trust that they are charging at the stated rate, but is it possible to measure this? For instance, what would happen if the probes were put on the charger itself, with or without a battery in it?

I haven't tried any of these things because, to be perfectly honest, I'm afraid that I'll blow something up. I imagine it wouldn't be quite that bad, but I don't want to damage anything just to test a theory, so I thought of ECF. Someone here surely knows the answers to these questions.

Thanks guys and gals!

 

[BardicDruid]

One guy told him that if he put the probes of his multimeter on each end of the battery with the meter set to measure amperage it would give him the battery's max discharge - that the battery would put out as much current as it is capable of.

This hopefully would pop the fuse in the meter, if not, you just cooked your meter, they only run on 5V internally at mAs.

Another guy though said that the only way to measure the current from a battery is if the battery is under load - that you have to put the meter "in series" with the rest of the circuit.

This is the proper way of doing it, but you have to figure out a way to get the positive probe (red) on the positive end of the batt and the negative probe (black) on the center pin to the clearo or carto, while at the same time maintaining the conductivity of the body of the mod.

When we put our batteries in the charger to charge, we trust that they are charging at the stated rate, but is it possible to measure this? For instance, what would happen if the probes were put on the charger itself, with or without a battery in it?

With a decent charger, the circuitry in the charger is trying to identify what kind of battery is connected and the meter is trying to read the voltage, at the same time. In other words they'll just run each other in circles and do nothing productive.

 

[mezzio]

"Another guy" is correct. Amperage ratings given off multimeters should be used under load. If you connect your meter up to a battery and try to measure amperage without it doing anything, it's going to read almost nothing.

Battery chargers generally will only charge at their set rate (1amp, 2 amps, 5 amps), whatever the manufacturer sets as the charge rate. You can pretty much guarantee you're getting that rate because everything in your house uses some sort of limiter to control the amps going to everything you plug in. Batteries do not charge at their discharge rate. Some LiPo chargers will allow you to change the charge rate, but the batteries meant for these chargers will tell you how many amps you can push in to the battery safely. If you try to charge a battery at 5 amps when it can only handle 2 amps, and the chargers internal circuits will stop the charge from happening.

 

[Baditude]

The following is from PBusardo's Taste Your Juice website:

A NOTE ABOUT C-RATINGS
The C-Rating of the battery defines the maximum draw (in amps) that the battery is capable of. To calculate the max amp draw you need the C-Rating and the mAh of the battery. For example a 2000 mAh battery rated at 10C would be:

Max Amp Draw = (mAh / 1000) * C-Rating

(2000 / 1000) * 10 = 20 Amp Max Draw

Note: Running your batteries at their C-Rating will decrease the overall life of the battery.

​

 

[Chakthi]

The following is from PBusardo's Taste Your Juice website:

A NOTE ABOUT C-RATINGS
The C-Rating of the battery defines the maximum draw (in amps) that the battery is capable of. To calculate the max amp draw you need the C-Rating and the mAh of the battery. For example a 2000 mAh battery rated at 10C would be:

Max Amp Draw = (mAh / 1000) * C-Rating

(2000 / 1000) * 10 = 20 Amp Max Draw

Note: Running your batteries at their C-Rating will decrease the overall life of the battery.

​

Okay, so I understand how that works when the 'C-rating' is known, but if you don't know the rating I'm now guessing that there is no simple way to find that out with a basic multimeter, correct?

Thanks for replies to all three people who answered. I learned a little something from each of you.

 

[Baditude]

Okay, so I understand how that works when the 'C-rating' is known, but if you don't know the rating I'm now guessing that there is no simple way to find that out with a basic multimeter, correct?

Some vendors provide the C rating or the amps in continuous discharge rating in the description of their batteries, but unfortunately most do not. I believe the vendors that cater to the flashlight crowd do so, like Lighthound and Orbtronics; probably others that I'm not familiar with. The guy who has the following blog has battery information like this for a few of the more popular batteries:

Battery Data | Deus Ex Vaporis

Most people who are interested in finding the amp rating of a battery are often most interested in the continuous discharge rating. I have those specifications for most of the most used IMR or hybrid batteries here:

Ohms Law Calculator

AW IMR
18650 2000mah 10Amp CDR
18650 1600mah 24A

Panasonic ​or Orbtronic hybrid
CGR18650CH (IMR/Li Ion hybrid) 2250mAh 10A
NCR18650PD (high drain-high capacity) 2900mAh 10A

Samsung hybrid (LiNiCoMnP)
INR18650-20R 2000mah 22A

MNKE IMR
IMR18650 1500mah 20A

Sony IMR
us18650v3 IMR 2250mAh 10A

EFEST IMR
18650 2000mah 10A

* AW IMR
18490 (1100mah) 8.8A

*AW IMR
18350 ​(700mah) 6A​

 

[Chakthi]

Thanks for the info Baditude!