Volvo XC90 Owner's Manual page 172

WARNING!
The battery contains oxyhydrogen, which
is highly explosive. Be sure that the evacu-
ation hose is correctly connected!
WARNING!
Batteries can generate oxyhydrogen gas,
which is highly explosive. A spark, which
can be generated if you connect the jump
leads incorrectly, is sufficient to make the
battery explode. The battery also contains
sulphuric acid, which can cause serious
burns. If the acid comes into contact with
eyes, skin or clothing, flush with large
quantities of water. If acid splashes into the
eyes, seek medical advice immediately.
Maintenance and service
NTN