Doc Wattson gauge for electronic devices.
 

a few weeks back I put together a new battery pack for my electric push lawn mower and I quickly realized that with the Lithium batteries that I wanted to know the state of charge, with lead acid the voltage sags so much as the battery pack runs down but that is not the case nearly as much with Lithium and running lithium until it's dead is not a good idea!
So I seemed to have two choices, a Doc Wattson or a Brain Drain, the brain drain is by far the slicker gauge and it can do so much more and handle more amps with a shunt, but the Doc Wattson was much cheaper and does what I need it to do for a push lawn mower!
So at all times it gives me the voltage, watts and amps, then while it is running it has a 4th line that switches between peek amps sense the last reset, minimum volts sense the last reset, KWH sense last reset and amp hours used sense last reset, resetting is done by unplugging the meter or by hooking a push button up to a small plug in the side of the meter.
Specs say this meter is good for up to 100 amps and 4 to 60 volts.
Brain Drain looks slick but the cost was more then twice as much, of course the brain drain can do things like have a speed input and can control the main contactor so it cuts power if you over speed or drop your voltage to low, things that would be nice to do on a lawn mower but not needed!
I really like that it will give me the peek amps and minimum voltage so I can make sure not to damage my battery pack, this seems like it would be useful for running without an alternator, assuming that you bipassed the gauge with the cable that goes to the starter.

https://encrypted-tbn3.google.com/im...WjtFZsPQ8sNC89

I have that same meter, but its called the Watt's Up meter. I haven't actually used it for anything because of its current and voltage limitations. But, it looks like quite the handy device.