Olympus BLM-1 LiIon battery test

The original Olympus BLM-1 LiIon battery vs. cheaper alternatives


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Summary

I tested the capacity of the original Olympus BLM-1 battery and of cheaper alternatives and measured the following (all betteries had a nominal capacity of 1500 mAh and were three months old):
These are the discharge curves (battery loaded with a 13.6 Ohm resistor):
BLM-1 battery discharge curves
It is possible that the capacity is higher if you discharge the battery over a period of five hours instead of three.

What does all this mean ?
See below for an in-depth discussion of the results and the test method.




Introduction

After purchasing the Olympus 8080 in July 2004 I faced the problem of getting a second battery without paying the ridicolously high prices Olympus is charging for its BLM-1 battery (70 Euro or more in August 2004 in Germany). After hearing positive reports I ordered two 3rd party BLM-1 batteries from an ebay seller in Hong Kong. The cost per battery was US $5.49 per battery and for the two batteries I ordered I payed a total of US $17 including shipping. The batteries arrived in 10 days. To get a more accurate idea of how long the 3rd party batteries last with respect to the original Olympus one, I recently ran a test.



Test configuration and procedure

Before the test each battery was discharged completely and then fully recharged. The battery was then loaded with two 6.8 Ohm resistors - total resistance was 13.8 Ohm. The drain current was therefore a bit over 0.5 Ampere on average. This is a high current - on average a camera like the Olympus 8080 for instance drains around 0.2 Ampere.

Test configuration

With this load it took between 80 and 140 minutes to completely discharge the batteries. Since I didn't have an A/D converter with a computer interface, to measure the voltages over time I used a standard digital multimeter and took automatically photos of it every 60 seconds using a camera control software:


Test configuration

Here the camera is connected to the computer with a USB cable and takes shots of the multimeter every 60 seconds.

This is an example shot:

Meter display

I have then entered manually the measurements into a table.

The capacity is obtained by adding all measured voltages and divide that by 13.6 (the resistance) and divide by 60. That gives you the capacity in Ampere-hours.

If you have a look again at the discharge curves, you will note that the voltage is not constant, and over a large period of time drops by about 10 mV per minute. Below 6.5 Volt the battery voltage collapses very rapidly (in less than 10 minutes) and the beginning of the steep drop region is at about 6.6 - 6.7 Volt.
Noise test results

It also appears that the 3rd party BLM-1 batteries have a slightly lower effective voltage than the Olympus original one. The difference lies between 200 and 300 mV.

The lowest recorded voltage with a BLM-1 battery was 5.4 Volt. Below this level the battery voltage drops to 0 in less than a minute.



© Alfred Molon 2004