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Uncle Peter · 26-03-2019, 00:02

Your battery would have to be really dead if the ECU were to lose all of it's fuel tables and maps and you'd probably be at the point where the immobiliser would have to be reset.

If it's a relatively modern car and depending on the car it's possible that the ECU is blocking startup if it's seeing less than 12v. You might be better buying an ECU saver which you can plug into the diagnostic port to protect the ECU's volatile memory while swapping out a second battery which can be charged up in the house.

26-03-2019, 00:02	#3
Uncle Peter 81-82-83-84 Join Date: Nov 2006 Location: on holiday by mistake Age: 54 Services: Vivid 200, Full House, V6 x2 Posts: 5,977	Re: Car battery backup. Your battery would have to be really dead if the ECU were to lose all of it's fuel tables and maps and you'd probably be at the point where the immobiliser would have to be reset. If it's a relatively modern car and depending on the car it's possible that the ECU is blocking startup if it's seeing less than 12v. You might be better buying an ECU saver which you can plug into the diagnostic port to protect the ECU's volatile memory while swapping out a second battery which can be charged up in the house.