Battery load test demo: internal resistance with one resistor

A worn battery can read fine at rest. The readings here are made up; in the app they come from your own multimeter over Bluetooth.

Phone simulation: Battery load test

SIMULATIONComing in an app update

A load test result in the app: AA NiMH GOOD under load, internal resistance 0.0425 Ω, under load 1.291 V, at rest 1.305 V

09.41

BackLoad testOW18B

Step 4 of 4

0 sClip the resistor on nowThe count starts by itself when the voltage drops.

3.92 Ω

red probe+AA · NiMH−black probe

Keep the probes on the battery's own ends.

At rest (saved)1.305 V

Now · no drop yet1.305 V

IF NOTHING HAPPENS FOR 15 SECONDS

The voltage did not drop. Check that the resistor is clipped across the battery. No result is given without a drop.

Cancel

0 sread at 2 sstops counting at 10 s

Measure againSee the result

BackAA · NiMHDone

Remove the resistor now

GOODUNDER LOAD

Holds its voltage under load.

Indicative limit: treat it as a guide.

Internal resistance0.0425 Ω

Good to 0.05 ΩWeak to 0.10 ΩReplace

Under load (2 s)1.291 V

At rest1.305 V

Current0.3293 A

Resistor3.92 Ω

Heat in the resistor0.43 W

Measure againShare

Freeze & capture

Next feature: Car battery test

About the load test

You measure a power resistor first, then clip it across the battery while the probes stay on the battery's own ends. The app sees the voltage drop, counts to two seconds, reads the value and tells you to remove the resistor. From the drop and the current it works out the internal resistance and gives a verdict.

The load test limits are indicative: treat them as a guide. There is no resistor load test for 12 V starter batteries; there the starter motor is the load (see the car battery test). The load test is coming in an app update.

On testnmeasure.app

iPhone and iPad (iOS 17 or later): free on the App Store. Android later.