I made a good purchase of 13 of these 5-AA-cell NiMh battery packs and have put 5 of them into a case which was left over from an aborted project long ago. Earlier I had put in 6 packs in it in series parallel for 12V nominal, but I changed the design to 5 packs in series for a nominal 30V. A Lucent DC - DC converter converts the battery voltage to a regulated 5V @ 6 A, accessed via two USB type A sockets. The project was also predicated on buying cheaply a 48V, 0.35A switching power power supply for the charger.
The charger has both a High and a Low current resistor current.
Charging is controlled by a Picaxe 14M circuit which monitors both the battery pack temperature and its voltage.
This is powered by the charger when charging but can also optionally be turned on during battery operation to check the battery votage, which is displayed on a row of four colored LEDs.
|Here are photographs
Here are the circuit diagrams
|Here is the code