Toyota prius Owner's Manual page 436

4-3. Do-it-yourself maintenance
 Before recharging
When recharging, the 12-volt battery produces hydrogen gas which is flam-
mable and explosive. Therefore, observe the following precautions before
recharging:
 If recharging with the 12-volt battery installed on the vehicle, be sure to
disconnect the ground cable.
 Make sure the power switch on the charger is off when connecting and
disconnecting the charger cables to the 12-volt battery.
 After recharging/reconnecting the 12-volt battery
 Unlocking the doors using the smart entry & start system may not be
possible immediately after reconnecting the 12-volt battery. If this hap-
pens, use the wireless remote control or the mechanical key to lock/
unlock the doors.
Start the hybrid system with the "POWER" switch in ACCESSORY mode.

The hybrid system may not start with the "POWER" switch turned off.
However, the hybrid system will operate normally from the second
attempt.
 The "POWER" switch mode is recorded by the vehicle. If the 12-volt bat-
tery is reconnected, the vehicle will return the "POWER" switch mode to
the status it was in before the 12-volt battery was disconnected. Make
sure to turn off the power before disconnect the 12-volt battery. Take
extra care when connecting the 12-volt battery if the "POWER" switch
mode prior to discharge is unknown.
Restart the hybrid system, depress the brake pedal, and confirm that it is

possible to shift into each shift position.
If the system will not start even after multiple attempts at all methods above,
contact any authorized Toyota dealer or repairer, or another duly qualified
and equipped professional.
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