Secondary car battery for alarm

StephenRyan

Hey everyone,

I have installed an alarm system w/ remote start in my car. Currently it is running off the constant 12v at the ignition switch but I want to ensure that if the car battery cable is cut or disconnected than a secondary battery (12A gel motorcycle battery) will continue powering ‘just’ the alarm, no start ability due to the size of the wires I’m limited to running (0.75mm2). I thought the alarm system I bought had backup battery functionality built-in but I bought the wrong model for that…

So my options so far:

I see some ‘intelligent battery isolators’ on the market but im not sure if/which ones would suit my application.
I thought of using a relay that only enables the secondary battery when the primary battery is disconnected but then theres the issue of charging the secondary while driving

I have tested with the primary battery disconnected and the secondary connected, the alarm works but obviously if you try to switch the ignition on, the gauges go mental and relays are clicking. I dont think it would be safe to run it like this though, maybe i’d need a separate regulator for the secondary battery but then i dont know how the car’s electronics would respond to being powered by 2 batteries with 2 separate regulators?!

Maybe Im overthinking this but any suggestions would be a great help,

Thanks

Stephen

Foxxie

A one-way diode so it can’t back-feed into the rest of the car. just for the alarm and charging leads to the battery. that way the battery will get charged. and also be able to power the alarm. but the battery won’t try to feed power back into the rest of the cars electronics/starter ect. not sure what options there are for that but there is probably something.