Car battery backup.
 

I drive rarely, so the car battery slowly discharges keeping the Engine Control Unit's memory intact.

In the past I used a battery disconnector to keep the charge up, but that meant poor starts after several days due to the ECU memory having been wiped.

What I'd like to do is either:

a/. connect a small 12v sealed lead acid battery to the car via the cigarette lighter socket, so that I could then disconnect the car battery to charge it from time-to-time, but retain ECU memory. The small battery would be recharged in the shed ready for use as and when.

b/. permanently fit a 12v sealed lead acid battery in the motor compartment, that would not go out of circuit when I use the battery disconnector to isolate the main battery. It would recharge in parallel with the main battery during driving.

My background is radio and electronics, not batteries and alternators. So could someone say whether either or both of the scenarios would work?

:dunce::dunce::dunce:

Re: Car battery backup.
 

One of these pehaps with option a). It would also recharge via the cigarette lighter.

Could perhaps be installed permanently under seat?

https://www.ebay.co.uk/itm/NP7-12-vo...-/111086402859

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.

Re: Car battery backup.
 

I use a trickle charger, less than 1 amp, on my old car that's currently garaged to keep the alarm/central locking and ECU alive.

Re: Car battery backup.
 

Pretty much this, all of the bikes and one car are on battery optimisers