For example, a tv remote needing two AA batteries instead of four AAA batteries.
In: 2
What voltage is needed? Most batteries (AAA, AA, C, D) in consumer electronics are 1.5v each. Most microchips run on ~3v or ~5v, so they need either 2 or 4 batteries.
How long does it need to operate? The size of the battery tells you how much energy it stores. The more stored energy, the longer it lasts. 8 AAA will run a portable stereo, but for way less time than 8 D batteries will.
A little more technical. The capacity of a battery is measured in amp-hours (Ah). A battery with 1Ah of storage (same as 1000mAh) will supply 1 Amp (1000 milliamperes) of current for one hour. Or 0.5A for 2 hours. I’m f your device has a constant load current of 400mA and you want it to run for a minimum of 17 hours, you need a minimum total capacity of 0.4A * 17hr = 6.8Ah. Combine that with your voltage requirements and off you go.
Some circuits need 3v but one AA is 1.5v. So two batteries are placed in series, or end to end, because you add voltages in series. But maybe the circuit only needs 1.5v but it needs to run longer than one battery can last. You place the batteries side by side in parallel and now you still have the same voltage but you’ve doubled the available energy that can be used per second.
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