A question for the tech-heads.
About Jags (not just F-Types) that have the dual battery stop/start system (ie pre 2016 when Jag switched to a single battery).
I'm having a "debate" on another forum with a 2014 XF owner who insists that the smaller secondary battery powers the starter motor for stop/start restarts (and that is it's only purpose), when I am fairly sure that the main battery is used for restarting the engine and the secondary battery's primary or even sole purpose is to power the peripherals (lights, ICE, A/C etc) when the engine has been stopped by the stop/start system. I read this somewhere, maybe on this forum, but I can't find it again.
I've also plowed through about a dozen pages in the Workshop Manual covering the batteries but nowhere does it clearly state which battery powers the engine restarts.
Anyone know for sure?

 

I have the small battery disconnected in my F-Type R 2014 and everything works correctly...

 

So have I, for the past two years and not a problem.
But that wasn't my question, what I'm trying to find out is "proof" as to which battery is used to restart the car when stop/start is working and has stopped the car.

 

[QUOTE = OzXFR; 1974758] Yo también, durante los últimos dos años y no hay problema.
Pero esa no era mi pregunta, lo que estoy tratando de descubrir es una "prueba" de qué batería se usa para reiniciar el automóvil cuando la parada / arranque está funcionando y ha detenido el automóvil. [/ QUOTE]

I think I do not understand you, because of my English. If you removed the old battery the Star / Stop does not work, right?

 

 

 

So what happens when we remove the small battery? I took it off just a month ago ...

 

 

Has ANYONE experienced glitches in electronics due to a voltage drop during an ECO Start? (Or are we all in Dynamic mode? )
My 1980s Ford told me it was time to check the battery because the radio would 'forget' my radio presets when it got weak. And, our 2002 Dodge permanently pegs the speedometer when the battery voltage drops.

The two batteries, aren't they wired in parallel?

 

 

 

So, when removing the small battery we also leave with "less force" the rest of the electronic things of the car? that is, we cancel the Star / Stop but also other things? so we need to have the main battery in top form, right?

 

All modern cars need good batteries.

 

Thanks DJS, dunno how I missed that bit!
Should clear up the debate on the other forum once and for all, although the member I am debating is fairly stubborn and has received written advice from his dealership that it doesn't work that way (ie that the engine is restarted by the secondary battery).
I suspect it is yet another example of the dealership "service advisor" not knowing what he/she is talking about.

 

 

Mine is dead for 2nd time, not on warranty any more. Probably pro rated. Start stop never bothered me but I don't miss it. Will not spend any real money to replace it.