Battery discharge curves

I wanted to buy some Sony VTC6 batteries, and I was wary of fakes, so I wrote a battery discharge calculator with an associated hardware component (just a simple current and voltage sensor). I then took some measurements of my known-good batteries, and the new ones I bought.

The methodology was the following: I connected the battery to the sensor, and the sensor to a configurable load. I set the load to draw a certain amount of amps until it reached a cutoff voltage, and then to stop. I then plotted mAh drawn versus voltage, as well as amps drawn.

The batteries I connected were in various states of use, and various configurations (for various reasons, I couldn’t test single cells). The configuration, state of the battery and provenance are mentioned below.

Here are the graphs:

Genuine Sony VTC6

This is a genuine (as far as I can tell) Sony VTC6, fairly used in high amp draw situations (I use it in my plane), in a 3S configuration:

curve_old-3s_2021-09-08_02-53-53.png

You can see that it output around 2600 mAh before I stopped it at 3V, which is quite good.

Here’s a brand new genuine VTC6, again in a 3S configuration:

curve_new-vtc6-3s_2021-09-09_13-06-52.png

This time I ran it all the way down to 2.8, and you can see it output the full 3000 mAh.

Fake Sony VTC6

This is a pretty blatantly fake “Sony VTC6”, brand new, in a 2S configuration:

curve_new-vtc6_2021-09-08_18-54-58.png

The performance falls off a cliff after around 3.6V, and it only outputs 1600 mAh before it dies completely.

Trying to draw 6-7A is even more spectacular (and it gets very hot to the touch):

curve_new-vtc6-6a_2021-09-08_23-57-29.png

Notice the huge voltage sag right as the load starts drawing.

White CNHL 4S 4000 mAh

This is a white CNHL 4S 4000 mAh LiPo battery, slightly used:

curve_cnhl-4ah-used_2021-09-11_20-29-53.png

You can see that it’s pretty decent, outputting nearly all of its nominal mAh, decently linearly, with a slightly faster drop after 3.7 V.


Last updated on September 12, 2021. For any questions/feedback, email me at hi@stavros.io.