The rechargeable battery of a motorcycle differs from a similar car battery in a smaller capacity. With a kickstarter, it works in much better conditions than an automobile. But even the kickstarter is sometimes unable to start the engine if the battery is discharged. This is known to everyone, thanks to the famous episode from the movie "Beware of the car".
Long before the battery requires another recharge, measure the voltage in the on-board network of a serviceable motorcycle with the engine running at medium speed. Write it down.
When the battery requires charging, remove it from the motorcycle. Draw in what polarity it was connected.
Become familiar with the electrochemical system used in the battery. It can be nickel-cadmium or lead. The former are usually used in motorcycles equipped with only a kick starter, the latter in motorcycles equipped with an electric starter or both. But there are also exceptions to this rule. Information about the electrochemical system of the battery is given on its case or on a sticker on it. Some modern motorcycles use lithium-ion and lithium-iron batteries. Do not try to charge them yourself.
Since motorcycle batteries have a lower capacity than car batteries, never use a device designed for the latter to charge them, unless the device has a charging current regulator.
Use a special laboratory power supply unit equipped with decade switches to charge the battery, which has a function to stabilize not only voltage, but also current strength. From domestic, B5-47 is suitable, in particular. Units without current stabilization function are not applicable.
Allow the battery to warm up to room temperature before charging.
Make sure there are no open flames or sparks around the battery.
If the battery is nickel-cadmium, multiply its ampere-hour capacity by 0.1 to get its charging current in amperes. Connect it to the power supply, observing the polarity. Set the ten-day switches to the voltage equal to the one that develops in the on-board network of a working motorcycle at medium speed, and the current equal to the charge current calculated by you. Turn on the power supply and charge the battery for 15 hours.
If the battery is lead-acid, charge it in two steps. First, set the current in amperes equal to 0.1 of the capacity in ampere-hours. Charge until the voltage reaches the result of multiplying the number of battery cells by 2, 4, expressed in volts. Reduce the charge current by half, then continue charging for another two hours.
Disconnect the battery from the power supply. Move it back to the motorcycle, observing the polarity.