E-Bike Battery Gauges: 0% Still Runs the Light

An e-bike battery gauge is a picture of voltage, or a count of current, drawn as a percent or as bars. The picture is not the watt-hours left. Bosch’s help page says five charge lights, an ice-blue bar for about 20 percent, a white bar for about 10 percent, orange below 30 percent, red below 10 percent, and a flashing red at 0 percent that means the motor is done and the light still has a reserve. Ride1Up’s support page, modified 13 February 2024, tells some riders they can set the voltage for each bar. A number you can type in is not a measurement. This desk did not put a meter on a commute.

Display Percentage

A percent on a cheap display is usually a voltage looked up on a table. Ride1Up says so, in the sentence that tells 700 Series riders to switch the screen from percent to voltage, and then adds that the voltage will still sag. Bosch does not show a percent at all on that help page. It shows bars, and the bars are not one size. An ice-blue bar is about 20 percent. A white bar is about 10. Five bars of 20 would be 100. A mix that includes 10-percent bars is not five equal slices. Do not add them until you know which color is on the bike in front of you. Orange below 30 and red below 10 are colors, not a second instrument.

Actual Voltage

Voltage is the number the display is already using, when it will show it. It is still not energy. Fifty-one minus 41 is 10, which is the span of the second 48-volt list. Forty-nine minus 40 is 9, which is the span of the first. Same brand, same “48 volt” name, two windows. Their peak for the second family is 52. Fifty-two minus 51 is 1, so the top of that sentence sits one volt above the highest number in the list. Their minimum usable is around 41.5, and the list includes 41.0. Forty-one and a half minus 41 is half a volt. The chart goes lower than the sentence next to it. A 13-cell lithium-ion pack at 4.20 volts a cell is 54.6. Battery University’s table for the common cobalt, NMC, and NCA cells is 4.20 full and about 3.60 nominal. Ride1Up’s peak on that page is 52, and they do not print a cell count. Fifty-four point six is not 52. This page will not invent the series count that would make them match.

Actual Remaining Energy

Watt-hours are volts times amp-hours, on the label, at the nominal voltage. The battery page is that sum. A gauge that says 50 percent is not half of that label unless the gauge counted current out of the pack and the pack is still the size on the label. A voltage table does not do that count. The middle of a lithium-ion curve is flat, which is why 46.5 volts shows up in both of Ride1Up’s 48-volt lists, next to different neighbors. Half the voltage span is not half the watt-hours. The range page is why the miles move before the bars do. This desk does not have a lab error, in percent, for an e-bike coulomb counter. An electric-car paper’s plus or minus 1 percent does not transfer to a five-bar bicycle display.

Behavior Under Load

Under load the voltage falls by the current times the pack’s resistance, and it comes back when the current stops. The display that is only a voltage table falls with it and then climbs. The battery did not refill. Ride1Up prints that recovery as normal. How many volts is the pack’s business. One film, below, reads a meter. It is not a class bicycle, and the two sentences in it do not match.

Last 20%

The bottom of the curve is where the voltage finally moves, which is why the last bar feels short. Bosch’s page puts orange below 30 percent and red below 10, and then a 0 that is not empty. Flashing red means no motor support, and reserve left for the light. The rider’s empty is the motor’s cutoff. It is not the cell at Battery University’s 3.00-volt full-discharge line, and it is not zero watt-hours. A lithium-iron-phosphate cell on that same table is full at 3.65 and discharged at 2.50, not at 4.20 and 3.00. A gauge drawn for one chemistry, read on the other, will call the pack empty while it still has a hill in it, or full while it does not. The last 20 percent of a bar graph is the manufacturer’s last slice. It is not a promise of one-fifth of the label.

Different Manufacturers

Bosch publishes colors and approximate percents. Ride1Up publishes voltages, two sets for the same 48-volt name, and a setting the rider can change on one of the families. A 52-volt chart whose highest printed number is 57 is a third dialect. Fifty-eight point eight would be 14 cells at 4.20. Their highest number is 57.0. The name on the chart is 52. Three figures, one row. A no-name display that will not show voltage, and will not say which table it used, is a picture. Compare two bikes by the watt-hour label and by a voltage taken at rest, not by whose bar looks longer in a parking lot.

Results

There is no accuracy number, because the two charts and the 0% light are not one test.

Read the gauge at rest if you are going to read it. Under power it is the sag, and the film that shows a sag also says 8 volts, 4 volts, and a subtraction that equals 1. At rest, use voltage if the screen has it. Then remember the table under that voltage is the manufacturer’s, and Ride1Up printed two of them for one name. Bosch’s 0 percent still runs the light, so the bottom of a careful gauge is a reserve, not a tank. None of that is a percent this desk measured on a road. A bar that you can set, and a bar that changes color at 30 and at 10, are the results that were actually published.