how to install back up battery

Does anyone have any recommendations for installing a back up battery for an alarm system?  Does anyone have suggestions on a type of battery or configurations to hook it up?KCjester

Maybe? 1)     Buy a YUASA maintenance free dry battery such as NP4-12 12V 4.0 Ah. It measures 23/4X31/2X4H. 2)     Use two SPDT 12V Constant Duty Relays Provide a fused constant voltage to both relays 85 via the car battery. Ground 86 of the relays. This holds the relay coils constantly active. #1 Relay, Break the alarm power wire and use 30 and 87. 30 being the input and 87 output. #2 Relay, Connect the Dry battery positive to 30 using a Diode. Connect 87a to 87 of the first relay and install a battery ground wire. From the alarm use a +12V low current output with a Diode, my alarm BLACK/ White wire, to the positive terminal of the battery to trickle charge the battery. The battery can be in the trunk if you wish to run wires. If the car battery cable is cut the voltage is lost and the backup battery supplies voltage to the alarm. Does this sound feasible? Knowledge is Indisputable, Opinions are Subjective.

I don't know what output from my alarm would be a low current 12v.  Could I use any wire from the alarm that provides 12 volts?KCjester

kcjester, The is no use for a back up battery to your alarm system. What you want to get is a back up siren. They cost about $35-50 way less than a battery and also serve the purpose.   If the power is cut and the siren is trigger it will continue to sound until it runs out of battery or you manual turn it off with the master key. Be careful whose advice you buy, but be patient with those who supply it.

I owe you a response, sooo! You will need a low current 12V for charging the battery otherwise the battery life will be severely impaired. I am not sure if you can use a resistor to limit the current to.5 amps If I were to implement this, I would put the stuff in a shoebox, including a siren that has been attached to the battery hot wire, and place it in the trunk. The alarm would stay energized; siren would also turn on when the main battery source is removed via blown fuse, cut cable or dead battery, so I would also add a kill toggle switch in the driver compartment to eliminate the siren or turn it off. The kill switch would be out of sight and used to turn the siren off, for service or for battery replacement. Before implementing, I would ask for advice from an EE or Tech that may be on this site since I am an ME. You also should consider the previous post of a backup alarm if it serves your requirements, as it sounds simple to implement. Knowledge is Indisputable, Opinions are Subjective.

thepencil wrote: kcjester, The is no use for a back up battery to your alarm system. What you want to get is a back up siren. They cost about $35-50 way less than a battery and also serve the purpose.   If the power is cut and the siren is trigger it will continue to sound until it runs out of battery or you manual turn it off with the master key.

This is the best advice, forget the battery backup to the alarm...what you care about is the siren. I have two in mine. One inside the car and one under the hood hidden away.