Rechargeable Battery Fixed Load Test

In the rechargeable battery fixed load test , the battery is loaded ( made to drive current ) with a fixed resistor or load. The resistor must be of an appropriate size ( wattage ) to ensure that energy is not lost due to heat.

From the data collected through a DAQ, we can calculate the total current and power ( watts or wattage ) delivered over a period of time.

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Fixed Load vs Constant Current Test

If you take a look at the Rechargeable Battery Fixed Load test page and the graph, you will see that the voltage is fairly constant over the greater part of the rechargeable battery discharge cycle. This is typical for a good NiMH rechargeable battery. In general, the NiMH rechargeable battery will provide a relatively constant current through a fixed load for the majority ( > 90% ) of its discharge cycle ( which is approximately 1.2v / R ).

The constant current test requires a circuit that can drain the rechargeable battery at the same current regardless of voltage changes in the battery. This is not trivial and requires a microprocessor based system with A/D and possibly D/A capability.

Examples of both these types of loads can be found in real life, but these test do not represent real world uses of rechargeable batteries.

Rechargeable Battery Review also recognizes this fact. That is why we have real world device tests to give you an idea as to how these devices perform.

Examples include:

AAA MP3 Test : This tests uses a single AAA rechargeable battery in a MP3 Player. The test can last beyond 15 hours and that classifies the test as a slow discharge test well below 0.1C.

AAA LED Test: ( started Aug 07 ) This tests uses a single AAA rechargeable battery in a high power LED flashlight. The test can last around 3 hours and that classifies the test as a high discharge test above 0.3C.

AA LED Test: ( started Aug 07 ) This tests uses a single AAA rechargeable battery in a high power LED flashlight. The test can last up to 4 hours and that classifies the test as a high discharge test above 0.25C.

More tests: That would be great. Make some suggestions as to devices, number of rechargeable batteries and why it would be a good test!

More information on Battery Fixed Load Versus Constant Current Test .