Not all batteries are made equal. Also well known that alkaline batteries are beating traditional zinc-carbon batteries in terms of output power and capacity. But how are really good these batteries? And are alkaline batteries better than their rechargeable counterparts?
Let's test some set of AA type alkaline batteries side by side with Ni-MH rechargeable batteries of same type (Sanyo Eneloop 1800mAh and Varta Ready2Use 2100 mAh). To measure discharge characteristics we will use well known IMAX B6 intelligent charger connected to Raspberry Pi single board computer.
All batteries are discharged by constant current (200mA) down to 0.8V. And below are discharge curves:
So alkaline batteries results are not so good as they are promoted by vendors! Despite to higher voltage in beginning (1.6...1.75V vs 1.3...1.45V), under load some time later alkaline battery voltage is falling below voltage of rechargeable battery.
Battery capacitance could be calculated from area under the discharge curve by integration, and multiplied by discharge current will result in total outputted energy (in joules):
|Battery||Energy, J||Capacity, mAh|
Last column is capacity of battery measured by charger (in mAh).
So, we can make some conclusions:
- Alkaline batteries are not so great. Only expensive ones have capacitance comparable to their rechargeable counterparts.
- More mAh isn't more capacity in terms of total energy (compare Duracell Turbomax and Sanyo Eneloop results).
- Alkaline batteries are well suited for low consumption devices (like remote controls, clocks, etc) and for extended temperature range devices (like outdoor sensors). If your device is high current and is not subject of low temperatures - rechargeable Ni-MH battery is your choice.
Some words about methodics
Charger data was logged by modified Niobos perl script running under Raspbian Linux. USB port was switched to 9600 8N1 raw mode using
$ stty -F /dev/ttyUSB0 cs8 -cstopb -ixon raw speed 9600
Text log file was created while battery discharging by command
$ b6_decode.pl < /dev/ttyUSB0 | tee out.txt
Resulting .txt files were transformed to .dat files with layout suitable to drawing graphs using gnuplot utility. Outputted energy was calculated by
If you have IMAX B6 charger connected to Linux box, you could make your own experiments with batteries using mentioned scripts downloaded here.