# Battery upgrade for 3v sensors

Been thinking about possibly adding external battery packs for some of my hard to get to sensors with one or more 26650 LiFePO4 batteries. 3300 mAh at 3.3v - 3.1v vs the typical 600 to 800 mAh at 3.0v - 2.0v or so the CR2 batteries have. Going with this setup they should last roughly 4 times longer. Anything glaringly obvious I'm overlooking?

The voltage is fine, I've used 3.7 LiIon batteries(CR2, CR123, 14500), charged to 4.2V in my sensors with no ill effects. The only consideration is that big azz battery can put out some serious current, and I don't know if that would damage the sensor or would the sensor's resistance cut the amperage down enough.
We need @JohnRob

I don't think batteries push current, rather the load pulls current. One of the reasons why a short which is basically infinite load is so fun.

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Batteries don't "push" current, current is pulled from the battery based on voltage and internal resistance of the circuit. You could plug your sensor on a 50 million Ah battery
(if that existed) and if the circuit needs 20mA, that it what it will take.

It's all in ohms law.

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Yea, I realized this a while back when I started needing dc power supplies for things. As long as the output was greater than is required, polarity was correct, and the voltage was happy then everything worked fine.

Ah, thank you both. So assuming the sensor internal resistance is 100 ohms and supply at 4 volts, we'd have 40 milliamps.
but if we connect a 40 volt battery, the the current allowed to flow would be 400 milliamps.
I think I get now

Assuming they aren't doing weird stuff inside the circuit yes. Buck converters split load resistance etc.

And POOF! no more circuit and a nice smelly smoke raising from it

That was actually what I did then I was 10 years old, got my radio that used 9 V battery and wrapped the wires from a corded lamp I had cut off, and plugged it in (while holding the radio). So after the scare of my young life, my dad gave me books from his university studies in Chicago. Never tried that again!

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