Honda EU10i Owner's Manual page 37

DC Application
The DC receptacle may be used for charging 12 volt automotive-type
batteries only.
In DC operation, turn the eco throttle switch to the OFF position.
1. Connect the charging cable to the DC receptacle of the generator
and then to the battery terminals.
To prevent the possibility of creating a spark near the battery,
connect charging cable first to the generator, then to the battery.
Disconnect cable first at the battery.
Before connecting charging cable to a battery that is installed in a
vehicle, disconnect the vehicle's battery cable. Reconnect the
vehicle's battery cable after the charging cables are removed. This
procedure will prevent the possibility of a short circuit and sparks if
you make accidental contact between a battery terminal and the
vehicle's frame or body.
Do not attempt to start an automobile engine with the generator
still connected to the battery. The generator may be damaged.
Connect the positive battery terminal to the positive charging cord.
Do not reverse the charging cables, or serious damage to the
generator and/or battery may occur.
34
CHARGING CABLE
(SOLD SEPARATELY: G, B, F, W types)