I'm trying to read the voltage of a 3S 11.1v LiPo battery with an arduino, so it can monitor the battery level and report when the voltage is getting low. The easiest way I've seen to do this is with a voltage divider. I've seen tons of "don't use voltage dividers" posts over the years, all for various reasons. My concern is the wasted power lost to heat that the voltage divider might draw.
If I have a low current drawing circuit hooked up, with a voltage divider to cut the voltage down to the range the arduino can read via the voltage reference pin, how much current will be used/wasted by that divider circuit? Is there a way to estimate that, without actually building the circuit and testing it? This is going in a device that is to run long term, and I'd hate to shave a large percentage of time off the runtime just to monitor the voltage.
Is there a better/more efficient way to read the voltage of a 11.1v lipo on a 5v arduino without using a voltage divider?