Circuit for backup battery connection with 12/24vDC vehicle battery

[maheshece28]

Hi guys,
I've a vehicle tracking modem which is going to connect in a vehicle has 12v/24vDC battery. I just need to connect a backup battery(12vDC) to modem for uninterrupt power supply i.e if 12vDC/24vDC battery goes off, want to switch over to backup battery. Also the backup battery should recharge with 12vdc/24vdc vehicle battery supply. Input power supply of the modem is 12v-24vDC and 2Amps. Is there any circuit? I googled but cant find the circuit for my electrical specs.

Thanks

 

[smijesh]

See the circuit

You should select 12V Battery terminal. Adjust 10K port for better performance

 

[maheshece28]

Thanks for the reply and circuit diagram.
Can i use this circuit for 24vDC vehicle battery?

 

[smijesh]

Then You should use 24V Backup battery and make 24V Relay instead of 12V, 10E 10W change to 20E 10W