Opel ASTRA Owner's Manual page 209

Vehicle battery discharge protection
3 128.
Disconnecting the battery
If the vehicle's battery is to be
disconnected (e.g. for maintenance
work), the alarm siren must be
deactivated as follows: Switch the
ignition on then off, then disconnect
the vehicle's battery within
15 seconds.
Replacing the vehicle battery
Note
Any deviation from the instructions
given in this section may lead to
temporary deactivation of the stop-
start system.
When the vehicle battery is being
replaced, please ensure that there
are no open ventilation holes in the
vicinity of the positive terminal. If a
ventilation hole is open in this area, it
must be closed off with a dummy cap,
and the ventilation in the vicinity of the
negative terminal must be opened.
Only use vehicle batteries that allow
the fuse box to be mounted above the
vehicle battery.
In vehicles with an AGM (Absorptive
Glass Mat) battery, ensure the battery
is replaced with another AGM battery.
An AGM battery can be identified by
the label on the battery. We
recommend the use of an original
Opel vehicle battery.
Note
Using an AGM vehicle battery
different from the original Opel
vehicle battery may result in a lower
performance.
We recommend that you have the
vehicle battery replaced by a
workshop.
Stop-start system 3 142.
Vehicle care
Charging the vehicle battery
9 Warning
On vehicles with stop-start
system, ensure that the charging
potential does not exceed
14.6 volts when using a battery
charger. Otherwise the vehicle
battery might be damaged.
Jump starting 3 247.
Warning label
207