I got my 40 amp battery charger for $150 brand new and i got 2 650 CCA batteries for cheap also. How can you say its a inefficient process ?? My house stereo is way louder than anyone's house stereo i have ever heard. It moves people's hair when sitting on my coutch and it even open my house windows about a inch when I'm listening to music. It also flexes my living room and kitchen walls so bad it has push the finishing nails out of the studs. This is all done by a visonik V159D6 sub in a sealed box with 750rms driving it.