Hyundai HL970A Operator's Manual page 26

Prevention of explosion
The following actions should be taken to minimize the risk
of explosion:
Preheating function is provided to certain machines that
are used in extremely cold environments.
Never use starting aid fluid in a low-temperature
environment as it can have an adverse effect on the
engine performance and may cause an explosion.
Do not attempt to recharge a frozen battery. Forcibly
recharging a frozen battery may result in an explosion.
Great care should be exercised when handling the
batteries. Never let a tool make contact with the positive
pole and the frame of the machine simultaneously.
Sparks may be generated, resulting in an explosion.
The voltage of the battery to be recharged should be
identical to the voltage of the recharger.
Incorrect voltage may cause overheating and explosion.
Do not use or charge the battery if the level of electrolytes
in the battery is lower than the minimum level.
Regularly check the electrolyte level, and refill the distilled
water to the maximum level.
Do not try to start the engine using an unsuitable booster
cable as it may result in an explosion and serious injury.
Only use the booster cable to start the engine in a
ventilated open space, as starting the engine with a
booster cable may generate inflammable gas.
When hydraulic equipment and piping are overheated,
inflammable gas or airborne particles may explode.
Make sure to protect and insulate such parts to prevent
overheating.
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