No, it will not harm your shaver.
However, it is a small possiblity that your shaver will rotate slower than when using 3V batteries.
battery produces voltage by
To increase voltage output when using more then one battery connect the batteries in series.
Because the original voltage of the battery weakens over time after using it for awhile making the voltage less then the original amount stated on the battery.
we can use a dc voltage directly from a dc source with parameters equal that of the battery
Batteries are storing charge or free electrons. The state is by nature a fixed voltage rather than a varying voltage. You can convert the battery charge to AC by using what is called an inverter.
Voltage can be calculated using Ohm's Law:Voltage = Current (A) x Resistance (Ω)Voltage = 4A x 3Ω = 12 VoltsTherefore, the battery is a 12 Volts.The power dissipated is Voltage x CurrentPower = 4A x 12V = 48 Watts
You can test a battery by using multimeter. Set the multimeter to the DC voltmeter setting and then place the leads of the multimeter across the leads of the battery. the multimeter will have a readout of the voltage.
If the 2nd battery is connected "in series" with the 1st battery, the voltage will increase & the motor will run faster. If the 2nd battery is connected "in parallel" with the 1st battery, the voltage will not change, but the total battery capacity will be greater & therefore battery life will be longer than when using just 1 battery.
Series.
Using standard cells with 1.5v nominal voltage, will take the total battery voltage too high and damage the circuits.
all vehicles will drop a certain amount of voltage when accessories are turned on, you need to determine how much voltage is being drawn by using a volt meter, also check charging system and battery condition, if battery is weak or charging system isn't providing enough voltage back to the battery, that can cause your problem and last but not least make sure your battery cables and battery posts are cleanThe battery's charge is low or something is drawing from it.
this sounds too simple to be asked. Or do you mean doing something else to the battery? if you can see the battery just disconnect the terminals using a spanner and replace the battery with one of similar voltage.