the speakers do not hook up to the battery, in a conventional system they hook up to the radio/stereo. if you have a more elaborate system they hook up to the amplifier. be certain what you are doing with this,or have someone familiar do it, it's a simple operation, but hooking wires up wrong can fry your electrical system, and even cause fire.
When hooking up a separate amplifier I prefer a back up on/off switch just in case I want the radio on but not the extra speakers, or a safety issue arises the need to kill the extra power consumption. Most amps today automatically turn them selves on when the radio is turned on. I install the switch in the line that tells the amp to start up.