For this round of testing, we gathered four of the most popular battery brands and tested five battery categories, including AAA, AA, C, D and 9-volt. Our objective was to find out which battery manufacturer offered the best value for your money. To assess battery performance, we used our custom-built battery test rig and timed the longevity of each battery, paying attention to their voltage output over time, and compared the difference in price per unit.
Battery performance and voltage drop
Measuring battery voltage output is more complex than simply sticking multimeter probes on the positive and negative ends of the battery. For instance, AA, AAA, C and D batteries are rated at 1.5 volts. If you measure voltage output directly on the battery, the reading may be close to 1.6 volts, which is generally a good sign for a new battery. Even batteries that are no longer usable can display a value equal to or higher than 1.5 volts when measured directly. The correct approach is to test voltage output under a load condition, such as when the battery is connected to a resistor or powering a device. Meet the CNET Labs Battery Test Rig:
CNET's custom-built battery test rig accommodates five battery types, including AAA, AA, C, D and 9-volt. The breadboards and connections allow for parallel and series circuit arrangements, depending on battery voltage. Gianmarco Chumbe/CNET
Components include two breadboards, one for 1.5-volt batteries and one for 9-volt, six motor fans that can be arranged conveniently either in series or in parallel, a switch for each circuit, one multimeter for voltage readouts, a chronometer and five battery slots for each type of battery: AAA, AA, C, D and 9-volt.
The testing logic is simple but revealing. To get the full picture, let's refresh ourselves with a bit of electronic basics. The number of active load components and the circuit arrangement depend on the type of battery under test. For the 1.5-volt group (AAA, AA, C and D batteries), we arranged the circuit loads in parallel, increasing the number of loads according to the capacity of the battery. This ensures that, regardless of the power source and number of loads, all load components are exposed to the same amount of voltage from such a power source — in this case, any of the 1.5-volt batteries. For example, AA batteries are tested using three motors in parallel, ensuring that all three motors get 1.5 volts each.
We use parallel arrangement on our test rig. From left to right, the 1.5-volt battery source (either AAA, AA, C or D), a voltmeter and motor array. The setup allows two motors to be active at all times, allowing the addition of up to five motors. Gianmarco Chumbe/CNET
For the 9-volt types, we arranged six load components in series. A series arrangement evenly distributes the voltage from the power source across all load components. Since each of our fan motors takes at least 1.5 volts to run, using a 9-volt battery provides 9-volt/6 loads = 1.5-volt per load.
Six motors are arranged in series. The 9-volt battery provides equal voltage distribution (1.5-volt) across each of the loads. Gianmarco Chumbe/CNET
Having established the basics, we proceed to testing. First, we ensure to connect our multimeter probes in parallel and take an initial voltage reading. Then, we make sure our circuit arrangement is adequate for the type of battery under test and flip the switch on. We start our timer and monitor the test, recording data readouts for voltage output under load every minute until the very last fan stops spinning. We run a "last man standing" competition. In our test logic, the battery that sustains the load arrangement the longest wins. The voltage drop allows us to see how efficiently the battery maintains a high voltage output given the test conditions. In this regard, the slower the drop in voltage, the better.
Here are the results, starting with an overall look at the average discharge time for each battery we tested. Longer bars indicate batteries that lasted longer in our test rig.
Here's a more detailed look at those results, with the specific, minute-by-minute dip in the average voltage readings for each battery during each test. Again, we're looking for the batteries that last the longest in this test, but more specifically, we're looking for batteries with as gradual a voltage drain as possible.
Enlarge Image Gianmarco Chumbe and Ry Crist/CNET
Price per unit
The cost of batteries can vary greatly depending on where and when you buy them. For that reason, we sought out the most economical source for each battery and compared the price per unit. Check out the table below, which we'll update regularly: