Remove the lefthand plastic cover. It is held in place by 4 plastic pins, these have a crosshead and 'should' unscrew enough to be pulled up. In practice, you may have to pry the center pin out.

Now check the alternator is being driven. Check the drive belt is not slipping or broken! If either is true replace the belt and skip ahead to the reassembly stage for how to fit a new drive belt.

Now Turn off the engine, All the power is coming from your battery you do not want to completely drain it!

Disconnect the Battery Terminal connectors. Always Disconnect the Negative (-)Terminal first! You do this so when you disconnect the Positive Terminal (+) if you wrench touches the bodywork you don't short out the battery as the whole of the car's bodywork is connected to battery Negative!

Tip Almost 100% of the time the positive battery terminal is coated in red; 100% of the time the negative battery terminal is coated in black. If you are unsure which terminal is positive or negative, the car battery has a + and - symbol molded into it near each terminal, that way you can differentiate the terminals.