Ebike batteries are DC power sources. If you need to test a battery, ensure that your meter actually has a DC voltage mode on it. Your multimeter should have these symbols on it:
The sinewave will only read AC
The straight line with the dashes will only read DC
Many multimeters are autoranging. They will automatically determine the voltage by just setting the mode. This is an example of one. This Fluke multimeter has a DC voltage mode, as well as a secondary DC millivolt mode for measuring tiny DC voltages. This is currently set for DC volts, and is ready to measure an ebike battery.
This meter has multiple sockets for inserting test leads. The two on the left are for measuring Amperage. The leads as positioned are ready for voltage measurement.
Some multimeters are manual-ranging. With these you need to manually select a range that covers the power level you'll be expecting. This Klein multimeter is currently set to read AC voltages as high as 600 volts. In order to read an ebike battery, you will have to rotate the mode dial left 3 clicks until you get to the 200 V DC indicator. From that mode, you can reliably read voltages between 20 V and 200 V max. Setting it to 20 V or less may damage the multimeter, blow a fuse, or cause it to read incorrectly.
With this meter, the black test lead goes to COM, and the red test lead goes into V
Most batteries have power switches on them. Ensure that the power is on before trying to read the voltage. If you attempt to read the battery on AC volts, it will erroneously show no voltage.
With the power to the battery switched on, make sure the red test lead is on the positive terminal, and the black lead is on the negative. If you reverse these, the multimeter will show a negative voltage (this won't damage the meter, but it does indicate polarity).
Ensure that your meter is set to the correct mode.
This meter is set incorrectly to AC volts: (note the false 0 volt reading)
This meter is set correctly to DC volts: (note healthy 47 volts from a partially discharged battery)
This meter has no DC voltage mode: (note the false 0.1 volt reading)
This sort of meter is entirely useless for testing batteries