I set Tom, one of our summer students, the task of making a battery tester to actually measure the capacity of disposable AA batteries. Tom created an active load for an AA cell which could be programmed using a small microcontroller to drain current in a controlled fashion. He made a prototype, then designed a PCB and finally built 5 identical battery test units. Tom wrote the embedded code so that each battery tester could autonomously take calibrated measurements as the batteries were drained. A separate piece of software ran on a computer to capture the measurements so we could analyse the data at the end of the test. Tom wrote a number of web pages to summarise the results and give more detail about how the tests were performed. The content of these pages have proved very interesting - we have had 65000 hits to date!
In May 2013 Channel 4 came to BitBox to films a repeat of the tests for a feature on alkaline batteries for the consumer program Super Scrimpers. The program went out in early May 2013. The results of both tests were surprising.
- don't bother buying zinc batteries (usually the cheapest). The don't last and are not cost effective.
- all alkali batteries have similar performances. Batteries that have lots of marketing behind them don't perform that much better. So, just buy the cheapest alkali cells that you can!
- lithium batteries do perform very well - if you actually need their performance.