May 17, 2011 -- posted by Evert Mouw
Author: Bob Westerbrink
Rechargeable batteries aged 6 years or older are, in general, garbage (this also is true for most car batteries). How good are your rechargeable batteries? You can test your batteries by measuring the time it takes until they are empty while they power a LED or something similar with a small resistance. It’s easiest to use a resistor.
You need a:
- battery to test
- resistor (R)
- 1.5V alarm clock (used as a timer)
- “voltage” meter (to measure the current)
The battery is connected to a series connection (circuit) of the resistor, the diode in forward direction, and the 1.5V timer. The diode limits the discharge of the battery to 0.6V to 0.7V. When the battery voltage drops to 890 mV then the timer stops and we denote the battery as empty. Now take some resistance for which we expect a discharge time of 10 hours when the battery is fully efficient (new). The value of the alarm clock after a full discharge gives an indication of the power delivered by the battery:
- Set the timer to 12:00h.
- Measure the current I after one hour.
- Make a note of the value of the timer at the and of the measurement.
- Capacity = (current I after one hour) x (time until timer stopped) x (0.89)
I few years ago I tested a few batteries with this method. I used 1900 mAh NiCd batteries which were modern at that time. The 1900 mAh batteries were 2 years old and the 1300 mAh batteries were 3 years old. The experiment should be repeated with new 2700 mAh batteries. You can download rechargeable batteries test results (Excel 2007 format, updated at 2011-05-18).
(Original tekst in Dutch, by Bob Westerbrink. Translated and edited by Evert Mouw.)