Battery for home made bike light


Newly Enlightened
Dec 21, 2006
I am building a battery for my home made bike light. I have the light figured out but not the battery. I know that the voltage is additive. e.g. 10 1.2 volt batteries in series will give me 12 volts.

Is the amperage additive as well. Will 10 4,000 milliamp batteries give me 40 amps? Or is it 4 amps?

To get run time do I multiply volts x amps and divide by watts??

Lastly, how do I connect a homemade to a charger?


Flashlight Enthusiast
Apr 14, 2005
Gothenburg, Sweden

When connecting in series, ten 1.2 V, 4000 mAh batteries will give you: 12 V, 4000 mAh

When connecting in parallel, ten 1.2 V 4000 mAh batteries will give you: 1.2 V, 40 000 mAh.

Series operation sums up voltage, parallel sums up capacity.

Please note that 4000 mAh is not 4 ampere (amp), it's 4 ampere-hours. Huge difference.

Hope it helps! Otherwise please ask!


Flashlight Enthusiast
Oct 31, 2002
given (example): cell is 1 V / 1000 mAh
2 cells in Series = 2 V / 1000 mAh
2 cells parallel = 1 V / 2000 mAh

light: 20 watt / 10 V = 2 A drive current
runtime: mAh of the pack / drive current
(then take at least 10 % less)

a personal opinion:
hitchhiking, biking, backpacking:
2 IMPORTANT points: weight, volumen
other points: runtime, cost, ease, "intelligence"
thats why, around here, very much people are changing to Li-Ion, and there is quite an easy, cheap way:
2 Canon 6600Mah Packs from e-bay, open + use the cells (4 in parallel, 4 of these packs in series to get the 14,4 V / 8800 mAh pack). Alltogether with a protection ciruit, using the maxim MAX1924VE. Full under-/overvoltage + current protection. For loading using some easy device with a 12 V lamp and a notbook power source.
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