I just have a simple question to ask. I'd like to measure battery life on a 9V external battery.
So I was looking at this SparkFun LiPo Fuel Gauge - TOL-20680 - SparkFun Electronics.
However, it seems only the MAX17043 is available. But it only takes up to 5V? Do I need to look for a MAX17044 or is there a regulator I am unaware of that will let it take the 9V battery and measure it? Or would I need to purchase a stepdown voltage regulator (buck converter) / look for another battery fuel gauge?
lipo and standard 9v batteries such as you get in a smoke alarm are very different. Decide what it is you want to measure. Measuring voltage is relatively easy. Current requires a resistive shunt.
I think you need to measure the current leaving the battery. The ACS712 may do this.
then your code should, at regular intervals take the average reading and work out the coulombs i.e if the current is 1 amp for 1 second then 1 coloumb has been discharge. count them and you know how many you should have left in the battery.
That is my basic understanding but it is probable I am wrong on technicalities! lol
But I feel like a multi-cell battery fuel gauge would work though?
If you look at the datasheet for the fuel gauge I linked, http://cdn.sparkfun.com/datasheets/Prototyping/MAX17043-MAX17044.pdf,
even though 2-cell is technically ~7.4V it says it should work for up to 10V on a MAX17044? So technically, would it work for a 9V lithium ion battery?
But maybe the lower threshold is set to a lower value instead of 6V of a 9V battery? I'm not too sure on the technicalities either.
If anybody else has some insight that would be much appreciated!
Not suitable for the small currents of a 9volt battery.
An INA219/226 breakout board might be more suitable.
They can measure voltage, current and compute power high-side up to 26volt.