Honda GL1800 2004 Owner's Manual page 168

Battery
Battery Charging
Refer to Saf ety Precautions on page 106 .
Be sure to read the information that came with your battery charger and follow
the instructions on the battery. Improper charging may damage the battery.
We recommend using a ''trickle'' charger for home charging. These units can
be left connected for long periods without risking damage to the battery.
However, do not intentionally leave the charger connected longer than the time
period recommended in the charger's instructions.
Avoid using an automotive-type battery charger. An automotive charger can
overheat a motorcycle battery and cause permanent damage.
''trickle'' charger
161
Servicing Your Honda