wiring up a backup alarm battery

I'm putting an aftermarket alarm/remote start in my car. Its an 89 civic with no stock alarm. I'm putting in 4 extra sirens. They're not going to be powered by the alarm but by a relay and triggered by the siren output. What I want to do is have a hidden battery, small maybe a motorcycle battery, as a backup in case the main battery cable is cut. I want it to be charged by the alternator but power drawn from it only if the main battery is disconnected. That way if the main battery is dead or disconnected, or the wires to the brain are cut, the alarm will still work. I'm fairly knowledgeable with electrical work and can follow directions very well and read a wiring diagram.".....um, is that wire hot?"

They make a back-up battery system specifically for alarms that triggers whenever power is lost to the alarm. The viper model is 515R or 511T (super loud siren)Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

I already have the alarm and the sirens. Are the model numbers you mentioned universal addons?".....um, is that wire hot?"

As far as I know, they are battery back-up sirens that will trigger if the remote starter loses power. They then require a special key (included) to turn off. Sorry, but I had to: LinkKenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

Simple - use a battery isolator. (EG "UIBI" - a relay energised by the alternator's charge light circuit.)

Not needed Peter, the back-up batteries mentioned have charging wires. To the first poster, 4 sirens sound no louder than 1 or 2 placed so the sound gets out! Law of diminishing returns, you're simply wasting your time and money. The correct answer is this. Mount a back-up battery siren in the rear quarter or inside the splash shield in the front wheel arch. In the other front wheel arch mount air horns and if the alarm you purchase has a separate low current horn output that can be set to oscillate, i.e. on-off-on etc, that's your answer and super loud!

As I said, I already have the sirens. As far as wasting money they were given to me. I want four because i'm not quite right in the head. oldspark, if I use a battery isolator am I correct in assuming that the alternator will charge the hidden battery but only the sirens will be able to draw power from it? I don't want the starter or any other accessories drawing power from it. Also, should I hook up the sirens AND the 12v constant to the hidden battery? Is it possible to set it up so that the sirens turn on if the battery cable is cut but none of the alarm sensors are triggered? Like a relay that's triggered if it doesn't receive a 12v constant, like if the battery cable is cut?".....um, is that wire hot?"

"oldspark, if I use a battery isolator am I correct in assuming that the alternator will charge the hidden battery but only the sirens will be able to draw power from it? I don't want the starter or any other accessories drawing power from it. Also, should I hook up the sirens AND the 12v constant to the hidden battery?" EDIT: oldspark, if I use a battery isolator am I correct in assuming that the alternator will charge the hidden battery but only the sirens will be able to draw power from it? I don't want the starter or any other accessories drawing power from it. Also, should I hook up the sirens AND the 12v constant to THE ALARM TO the hidden battery? ".....um, is that wire hot?"

Yes. The aux/secondary battery is isolated from the main when the alternator is NOT charging (or the IGN is off; the relay is powered from the IGN-on alternator's charge-light circuit). Hence loads connected to the aux will not drain the main battery. It sounds like your system has an inbuilt battery so that may not be needed. The alarm could be powered the same way (from the isolator relay), but then you use the alarm or siren's battery. Add the 2nd/aux battery if that isn't enough, or if you want to conserve the alarm batteries.