Caveat: I wouldn't charge a battery indoors.
A battery represents a heavy mass of chemical and electrical energy. It should be treated as a fairly dangerous object if it makes its way into your home. Some of the risk factors include:
Heavy: a car battery is a heavy object. Ensure that it is in a stable location with no change of tipping or falling because it is full of ...
Acid: a car battery is full of sulphuric acid. Ensure that is has no chance of tipping, spilling or otherwise expelling acid onto people, pets, valuables or even many metals. Remember, you are about to make the situation even worse by introducing ...
Electricity: be very careful with the terminals of a car battery. There are plenty of amps in there waiting to jump into a conductor and make enormously exciting and dangerous sparks. Keep in mind that when charging a car battery, it will produce hydrogen gas of some concentration. Ensure that the environment is well ventilated because otherwise there's an excellent chance of a dangerous ...
Fire: have a fire extinguisher in your hand. Note: you will have to make a judgment call on what type you need: what will the hydrogen ignite and how will you put it out? Where will the acid go when you start hosing it around with the extinguisher?
If I were forced to do this inside my house, I would put the battery in a large Pyrex casserole dish on the floor, run the charger from a GFCI outlet (to act as an additional ciruit breaker) and keep the fire extinguisher in my hand.
I would also wait until my wife was not home and I would not tell her later about the dumb thing I did today....
In all seriousness, what I would do (and have done) is to connect the battery charger to the battery while it's still in the car. Then I would plug the charger into an extension cord (or series thereof) until such time as I could reach a plug with main power. The risks of a car battery inside the house are significant and the benefits (convenience? hardly!) are small enough that they're difficult to measure.