Honda EU26i Owner's Manual page 36

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 vehicles grounded battery cable. Reconnect
the vehicle's grounded 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.
Batteries produce explosive gases: If ignited, and explosion can
cause serious injury or blindness. Provide adequate ventilation
when charging.
CHEMICAL HAZARD: Battery electrolyte contains sulfuric acid.
Contact with eyes or skin, even through plathins, may cause severe
burns. Wear a faceshield and protective clothing.
Keep flames and sparks away, and do not smoke in the area.
ANTIDOTE: If electrolyte gets into your eyes, flush thoroughly with
warm water for at least 15 minutes and call a physician
immediately.
POISON: Electrolyte is poison.
ANTIDOTE
External: Flush thoroughly with water.
Internal: Drink large quantities of water or milk.
Follow with milk of magnesia or vegetable oil, and call a
physician immediately.
KEEP OUT OF REACH OF CHILDREN.
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