Hi, on reflection I should have chosen a better title for this thread, probably "how accurate is the battery charge indicator?" The short answer is "not very". This is confirmed by forum comments and a few reviews like this one.
Initially I suspected that a voltage setting in the display was incorrectly set as you suggest, but I have been unable to find such a setting and if it were set to 36 volts then my 48 volt battery would register full charge throughout its 41v-54v cycle. Instead it has dropped one bar when the battery is just under 50% charge (76 miles). It is what it is so I am fitting a small digital volt meter to help me judge the state of the battery.
The battery inicator is very accurate. Only people that don't understand how it works say otherwise. It's basically a voltmeter that tells you when the voltage crosses various boundaries. Tht was explained by Woosh above. It uses a voltage divider to indicate to the LCD's CPU an actual voltage. The CPU uses software to send a repeatble instruction from its software to the LCD so that each bar on the display will change at exactly the time the battery voltage reaches the condition for each one. You can check it with a voltmeter, and you will find that it's consistent and accurate. It's up to you how you interpret and use the information, which is where the inconsistency comes in.
Battery voltage is not a good indication of range because not only is the voltage non-linear as it discharges at a constant current, but it also varies according to how much current you take fom the battery, which is varying all the time when you have a torque sensor system. When you pedal hard, the current will increase and the voltage will go down, then the voltage will bounce back up when you stop pedalling or pedal with less effort. Also, like Woosh explained, the motor's power decreases as the battery voltage goes down, so riders tend to demand more current from the system by pedalling harder, which causes increased voltage sag. In practical terms, that all means that the battery goes down slowly at first, then accellerates downwards during its discharge cycle.
To stop bars flashing on and off as you pedal, the software includes a damping factor, which is basically a moving average of the voltage that has the effect of averaging out and delaying the response of the battery level indication in the LCD.
To summarise, the LCD is not a range-meter. It's a voltmeter. To estimate your range at any time you need to understand how hard you're likely to be pedalling for the rest of your journey and how much hill-climbing you will be doing, and whether you expect to change your speed. No computer can know those things. What you will always know is exactly what voltage is in your battery when any segment goes out.
As suggested above, if you want an accurate indication of how much battery charge you have left, you can use a wattmeter in conjunction with the LCD. You can see at how many watt-hours you've used when each segment goes out, which will be consistent as long as it doesn't happen at a ime of excess voltage sag, like when hill-climbing. You can then interpret each bar on the display as a known percentage of charge remaining, and, as others have mentioned, there won't be much charge left when three of five are out.
I say again from my vast experience that if you do 60 miles on any electric bike and the LCD still shows all bars, either something is wrong or you did something exceptional that a normal e-bike rider wouldn't do, like riding with the power switched off or an exceptionally flat ride with the wind behind you. It can't just happen without explanation and you confirmed that you average 10 mph, so it wasn't that you were riding over the 15 mph cut-off, which would explain how that can happen with a fit rider on a fast bike, and your recumbent trike gives no advantage at that speed. In fact its additional mass and roolling resistnce would be a disadvantage. You should check the function of your battery indicator with a voltmeter.
When you said that the first indicator went out at 50% charge, that doesn't make sense to me. How did you figure out how much charge was left without a wattmeter? Also, the indicator levels are fixed by the hardware and software. The only way it could happen is if a wrong resistor were soldered to the PCB, but I never heard of that. I'm losing sleep over this. Please give an explanation so that I can make sense of it all.