Constant Current 1
Most electronic devices like digital cameras, GPS or portable audio run at a constant current. If the current drops when the battery is exhausted the device compensates by slowing down.
To achieve consistent results a Maha MH-C9000 charger analyzer
was used. Using
this it is possible to charge and discharge batteries at specified
up to 15 charge/discharge cycles.
Constant Current 2
A Computerized Battery Tester made by
Mountain Radio was used. Using it all AA size batteries tested were
constant 2 Amps (AAA 0.8Amps) down to 0.9v. Although
digital cameras usually run on a max of 1.2 Amps, the higher current
was chosen to obtain results quicker.
Watt-hours vs mAh and Simple Run Times
Rechargeable batteries are ususlly rated in milliampere-hours (mAh), a measure of how much current they can provide over time. A rating of 1600 mAh means that the battery should theoretically be able to supply 1600 milliamps (mA) for one hour, or 160 milliamps for ten hours, etc. The best NiMH AA cells today carry ratings of 1800 to 2700 mAh.
mAh is really only part of the story. What is more important is how much total energy a battery can deliver.
Energy is measured in Watt-hours, the product of voltage and current over time, or volts times amperes, measured over hours. (A milliamp is 1/1000 of an ampere.) To measure total energy, we need to measure the voltage and current moment by moment throughout the battery's discharge, multiply the two values together, and total up all the individual readings.
Further Fallacies of mAh" The standard way of measuring mAh gives wildly optimistic values when compared to what the batteries actually deliver in typical digicam usage. The problem is that digicams gobble power in big gulps, while battery-testing standards measure power delivered in small sips. Batteries are much less efficient when driving heavy loads than light ones. Thus, even if a manufacturer tests and reports their batteries' capacities truthfully according to the accepted standard, the resulting numbers may have little to do with how well the batteries perform in real-world digicam usage. " The Great Battery Shootout! by Dave Etchells
Because of this load-dependent behavior, I set up my
battery test system to run
the batteries under loads closer to those seen in typical digicams. As
result, the mAh capacities I measured are generally quite a bit lower
manufacturer's claims, but do give a much better idea of how the
do when plugged into an average digicam
The tests were repeated untill the results were within 2% of each other for at least 3 runs giving a standard deviation of less than 2%
NOTESAs my aim was to get the results to 2% or less certain precautions had to be done. The terminals in the battery holder had to be made from copper circuit board as the terminals in the plastic holders were found to give a small but significant resistance.
Battery terminals had to be cleaned before each days testing.
The wire between the battery and the battery profiller circuit had to be heavy copper and soldered to the terminals in the battery holder.
Charging had to be uniform. Batteries were charged using a Maha MH C401FS charger then left on trickle charge for at least 2 hours.
Links to Battery Testing SitesImaging Resource
Aqualab: Which Battery Will Do