I have installed an Android entertainment system in my car. The problem is that it gets activation signal through ACC line and it turns off while cranking the engine.

I will use the ignition line to send the activation signal so it won't turn off while cranking but I'm afraid that the voltage drop of the battery and the possible voltage spikes will create issues.

I was thinking to install a second small battery for the android system to give power only while cranking. The battery will be connected through a relay and a diode with the +12V line and when the ACC cuts off the relay will isolate the second from the first battery. That way the system will be powered from the second battery for a few seconds while cranking and the second battery will be charged while the engine is running.

Could I use a simple UPS 12V 1.3Ah or 2.4Ah which is small enough to fit inside the dashboard? What should I take care of? A schematic will be very useful. I found this schematic but it uses old type NiCd batteries. I'm concerned about the charging process and how effectively and safely the car will charge the second battery.

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  • Is there no manual telling you what wires you need to splice into? If you follow all the steps using the instructions there should be nothing wrong with it. Unless something else in your car is broken or not supplying enough power/current. Or is this system not meant for a car?
    – Granny
    Commented Mar 2, 2018 at 15:08
  • The system is designed to work as I described. It turns off while cranking to allow more power from the battery to be delivered in the engine. I want to change this behaviour by using a second battery to keep alive the entertainment system for a small time period (while cranking)
    – John
    Commented Mar 2, 2018 at 15:13
  • 1
    Why not use a capacitor? The capacitor should hold enough charge to accomplish what you are wanting, plus there's not worry about over charging a capacitor. A capacitor is going to have a lot longer life than any type of rechargeable battery would as well. A capacitor of sufficient size is going to be way smaller than a battery would be, making it a lot easier to place within the dash. Commented Mar 2, 2018 at 15:19
  • This type of question has been asked before search for split charge system...
    – Solar Mike
    Commented Mar 2, 2018 at 15:33


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