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1. Check the contact on the battery terminals.

2. Check the integrity of the onboard power supply fuse.

Usually, it is located in the starter relay block not far from the battery and its operating current is 20-30 amperes. You can find it along the red thick wire coming from the positive terminal of the battery;

3. Try to check the voltage on the battery.

Without devices, this can be done as follows: try to get the low beam or high beam lamp from the headlight and briefly connect it to the battery terminals. If the battery is charged, the lamp will shine brightly. If the lamp shines dimly or does not shine at all, then the battery is discharged.

If your motorcycle is equipped with a battery discharge indicator of the ML-IND type, then it will intermittently blink when the power on the battery terminals decreases.

4. Battery discharge is not a cause, but a consequence of a malfunction of one or more elements of the charging circuit (generator, relay-regulator, battery and wiring).

Unfortunately, not one of the aforementioned elements can be repaired in road conditions, therefore, the complexity of the situation can be minimized by "lighting" from the car. But at the same time, one must not forget that immediately after a successful start, it is necessary to disconnect the wires from the battery (if it is a car), since it is possible to disable the voltage regulator relay. The best option, of course, would be to replace it with a similar charged battery.
If you are lucky enough to replace or charge the battery, try to drive to the nearest service center using only battery power. To do this, locate the fuse box and remove the low beam fuse (during daylight hours). This will give you the opportunity to save energy and drive the extra 10-20 km.

5. Once you can locate a multimeter or voltmeter, you can reasonably be able to determine the cause of the charging circuit malfunction.

To do this, put the multimeter in the DC voltage measurement mode and measure it at the battery terminals. With the engine running, the voltage should be at least 13.5-14.5 volts. If the voltage is below this value, then proceed to the next diagnostic stage - checking the generator.

6. To check the generator's performance, it is necessary to find the connector for connecting it to the voltage regulator relay.

As a rule, a loop of three yellow wires comes out of the engine, ending in a three-pin connector.

It is necessary to disconnect this connector and measure the voltage between all contacts with the engine running. For a normally functioning generator, they should be at least 40-50 volts between the contacts of each of the windings. The voltage difference between the windings should not be 2-3 volts. If there is no voltage between the windings or is very different, then the generator may be out of order.
The next step in the test is to check the resistances between the generator windings. In resistance measurement mode, measure the resistance between the generator windings. It should be 0.6-2 ohms.
Next, we check the resistance between the windings and the "mass" of the motorcycle. To do this, we measure the resistance between each contact of the generator connector and the "ground" of the motorcycle. It should be endless (no ringing). If one of the windings "rings", then this indicates a short circuit of the generator winding to the "ground" of the motorcycle.
If you find a generator malfunction, then do not try to repair it on the road - it is useless! In this case, leave the connector disconnected from the regulator relay and continue driving using only the battery.
If the generator is in good condition according to all the above-mentioned signs, then look for the problem in the voltage regulator relay.

7. The voltage regulator relay can be checked in non-stationary conditions as follows:
Disconnect the connector from the regulator relay to the battery (as a rule, these are red and green wires). Connect the head light bulb to these wires from the output of the regulator. When the engine is running, it should glow brightly. If this does not happen, then with a high degree of probability we can talk about a malfunction of the relay-regulator. All parameters can be checked only in the service center at a special stand.
In this case, you can continue driving by first disconnecting the relay-regulator from the connector. In this case, the motorcycle will be powered only from the battery.