12 volt automatic changeover switch

Hi All can any body Post a circuit of 12 volt automatic changeover switch. I am even ready to pay some amount if anybody able to make it for me. Purpose is i have 2 battery Banks and currently i am manually switching it to 2nd one. I need to automate it so that switching is done automatically.

look at ckt here is working...
here switch is acting as changeover switch. i.e when u dont give 12v to it ,its in normally closed mode..it means 2nd battery is connected.
So whenever u want to switch from 2nd battery to 1st battery then just give 12v to switch i.e, turn on relay ,now 1st battery will be connected. Thats it!!!
here is relay -

I have not tested this circuit, but the principle should work !
Some values may need adjusting, ie change R1 to 150 ohms.