Alternate Battery

Hi hot_shot_guy123, the simplest way to add the alternate battery (if not a back-up battery) is to connect it parallel to the existing battery in the vehicle. If your concern is someone disconnecting the main battery, you can connect the positive terminal of the new battery to the B+ side of the alternator at the alternator (B+ side of alternator connects to positive terminal of existing battery) and connect the negative terminal to the chassis of the vehicle, then connect the 12V B+ lead of your alarm (and accessories/sensors) directly to the alternate battery.

If you're looking for a back-up battery for your alarm, there are many available and often at a fraction of the cost of a nice car battery. Either option is an easy install.

the12volt

Hi hot_shot_guy123,

I'd recommend at least an 8 gauge lead or better if you mount it in the trunk to keep it charged, by the way the trunk would be my first choice mainly because of size and the ability to conceal it. Yes, I would use terminals instead of attempting to solder directly to the battery. The B+ side of the alternator has a lead going directly to the positive terminal of your exisiting battery and I'd connect the second battery's positive terminal to it if you do not want to connect to the existing battery's positive terminal. Either connection will keep the second battery charged. Connect the second battery's negative terminal to the chassis. If you add this second battery, be sure to fuse the lead at each end where you connect to the alternator or existing battery and at the new battery itself.  

For back-up batteries, they come in a variety of small sizes that are easily installable in the interior of the vehicle that are adequate in supplying power to an alarm system. I'd first check with the manufacturer of the alarm you currently have before looking elsewhere.

the12volt

Thanks for your help, I'll be starting on that little project shortly.

  Sandro.