The "normal" minimum is around 3V, but I've seen protection boards touting 2.5V, a bit too low for me. My DelTang receivers shut off at 3V for a 1S arrangement, 6V for a 2S arrangement, etc.
Voltage drop-off with Lithium type batteries is a little worse than with NiMH types, which is why I prefer using a voltage regulator to maintain a constant voltage. IMO, since batteries have more capacity today than just a few years ago, I think performance is more important than the 10% or so loss in efficiency because of the regulator.
A 2S arrangement I'm using with Pamasonic 18650 x 3400mAh batteries (and 12V step-up voltage regulator) has 3 wires out to the side of the trailing (passenger) car. I use this connection to both slowly balance charge the batteries and occasionaly check cell condition. It is NOT recommended to fast charge batteries using the balance wire connection. eBay has several battery checkers that will do the job, around US$3-4.
Last edited on Thu Jul 12th, 2018 03:29 am by dan3192
Here's the performance curve for the 26650 battery.
If you know how much power your engine uses, you can estimate run time.
The slower the drain on your battery, the less it will heat up, which promotes longer battery life.