BP511 Battery Pack Load Tests

Updated 19 March 2006


I purchased my first digital camera, a Canon D30, in December 2001.
I later upgraded to a 20D, bought my wife a 300D, and handed down
the D30 to my daughter for her nascent photography business. My
daughter takes more exposures by far than the rest of us. She has
complained lately than many of the dozen or so batteries in our
pool (shared in common among the three cameras) are not holding up.

After some Internet research, I learned that Lithium-ion batteries
like the BP511 wear out after a few years. I decided to build a
text fixture to characterize our collection of batteries. I also
bought four new batteries from SterlingTek, anticipating that many
of our current batteries would prove worn out.

Test Fixture

Photo of test fixture

The test fixture consists of a laptop computer running OpenBSD 3.8,
a DI194RS RS232 serial port data acquisition module from DataQ Instruments,
and a breadboard containing a 50 ohm load resistor and a power MOSFET
switch. The load switch is controlled by one of the data outputs
of the parallel printer port on the laptop. The final element of the test
fixture is a C++ program I wrote to drive the test fixture and capture
the battery voltage.

Test Procedure

  1. Charge battery on Canon CA-PS400 charger.
  2. Top off charge for at least one hour after LED stops flashing.
  3. Connect battery to 50 ohm load resistor.
  4. Measure and record voltage across load resistor once a second.
  5. Calculate load current I=E/R once a second.
  6. Terminate test when battery voltage drops to 6.0 V (3.0 V per cell).
  7. Calculate battery capacity from the sum of all current samples.

NOTE: Test runs prior to the evening of 14 March 2006 terminated on
a battery voltage of 5.2 V. This caused the underdischarge protection
circuit to trip on one battery. Those earlier discharge curves
indicate a negligible amount of capacity between 6.0 and 5.2 V.

Test Results

Battery   Description       Purchased   Nominal    Measured   Plot

1         SterlingTek       3/2006      1800 mAh   1225 mAh   1.pdf
2         SterlingTek       3/2006      1800 mAh   1221 mAh   2.pdf
3         SterlingTek       3/2006      1800 mAh   1149 mAh   3.pdf
4         SterlingTek       3/2006      1800 mAh   1274 mAh   4.pdf
5         SterlingTek       11/2004     1300 mAh   1101 mAh   5.pdf
6         Canon BP511       ?           1100 mAh    420 mAh   6.pdf    RECYCLED
7         Canon BP511       ?           1100 mAh    539 mAh   7.pdf    RECYCLED
8         Canon BP511       ?           1100 mAh    780 mAh   8.pdf
9         Polaroid PR511L   ca. 2002    1100 mAh    479 mAh   9.pdf    RECYCLED
10        Polaroid PR511L   ca. 2002    1100 mAh    866 mAh   10.pdf
11        Polaroid PR511L   ca. 2002    1100 mAh    867 mAh   11.pdf
12        SterlingTek       11/2004     1300 mAh   1118 mAh   12.pdf   DONATED
13        Canon BP511A      11/2004     1390 mAh   1257 mAh   13.pdf
14        Canon BP511       ?           1100 mAh    977 mAh   14.pdf
15        SterlingTek       11/2004     1300 mAh   1127 mAh   15.pdf   DONATED
16        SterlingTek       11/2004     1300 mAh    999 mAh   16.pdf
17        Polaroid PR511L   ca. 2002    1100 mAh    380 mAh   17.pdf   RECYCLED
18        SterlingTek       4/2006      1800 mAh   1347 mAh   18.pdf
19        SterlingTek       4/2006      1800 mAh   1359 mAh   19.pdf
20        SterlingTek       4/2006      1800 mAh   1370 mAh   20.pdf
21        SterlingTek       4/2006      1800 mAh   1351 mAh   21.pdf
22        SterlingTek       4/2006      1800 mAh   1355 mAh   22.pdf
23        SterlingTek       4/2006      1800 mAh   1291 mAh   23.pdf
24        Canon BP511       ?           1100 mAh    998 mAh   24.pdf

NOTE: The good batteries all produce a fairly flat discharge curve with
a sharp knee at the end. The bad batteries produce a discharge curve with
a steady slope, suggesting a high internal resistance. This high internal
resistance is said to be caused by internal corrosion, and is the usual
failure mode for Lithium-ion batteries.

NOTE: Some have interpreted this exercise as a slam on SterlingTek.
Not so--I have been very satisfied with their batteries. They are at least
as good as Canon originals. Sadly, most capacity claims from most battery
vendors are exaggerated. Caveat emptor!

Battery Links

Questions or comments to phil@munts.net