Honda CLARITY 2021 Owner's Manual page 482

uu12-Volt BatteryuCharging the 12-Volt Battery
Charging the 12-Volt Battery
Disconnect both battery cables to prevent damaging your vehicle's electrical system.
Always disconnect the negative (–) cable first, and reconnect it last.
480
112-Volt Battery
When replacing the battery, the replacement must be
of the same specifications.
Consult an authorized Honda Clarity Fuel Cell dealer
for more information.