Rechargeable Battery Fixed Load Test

The Rechargeable Battery Fixed Load test is a common test used by most battery manufacturers. 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. What might differ between manufacturers is the value or number of the resistive loads being tested.

The Rechargeable Battery Fixed Load test method allows for an easy method of calculating current and energy because there is one fixed value or variable in the equation at all times.

The basic calculation in use is Ohm’s law : I = V / R.

From the data collected, we can calculate the total current and power ( watts or wattage ) delivered over a period of time. We use a dead battery (cut-off) voltage of 0.8v for all our measurements. Others may use 0.8v, 0.9v or 1v. This does not matter as there is little energy delivered after 1v when compared to the life cycle of the battery. What is important is consistency and that each rechargeable battery tested is treated equally.

The total amount of energy delivered by any battery drops as the battery is forced to work harder at higher and higher rates. The table below shows that the Ni-MH rechargeable battery has a relatively flat voltage during its use.

• At 9.7 ohms, the current at 1.2v is = 1.2v / 9.7 ohms = 0.124 Amps
• At 4.7 ohms, the current at 1.2v is = 1.2v / 4.7 ohms = 0.255 Amps
• At 3.4 ohms, the current at 1.2v is = 1.2v / 3.4 ohms = 0.353 Amps

If you check out some of the results provided in the AA battery section, you will see that total battery energy does drop as the battery is made to work harder and harder ( in this case, a lower value of R makes the battery work harder ).