I want to replace my 2nd battery with a Lipo 4 battery so I can run a fridge and other accessories, My car has the larger 2nd, stop start , battery . I understand the car has a smart alternator, and I am informed that I will need a DC to DC charger.

So far I think the 2nd battery only comes on line when the engine is stopped, although I have heard that it is joined in parallel when cold starts are required,

It seems if the battery is isolated and not in the circuit with the AGM main battery then I should be able to install 100 amp hr deep cycle Lipo4 to meet my needs.

I am no auto electrician , have had lots of different inputs , but no one seems to know for certain if my logic is correct. I am also unsure what the output is for the alternator , or if in fact I need a DC to DC charger.

Would appreciate any thoughts on this. M16 SVD8 ,4.4 HSE with a few extras, Sold R50 , Wife SQ5 , BMW R1200GSW.

Try these guys, if they dont have answers to your questions then i don’t think anyone will!

http://www.traxide.com.au/ 2003 BMW M5 - 5 Litres of V8 Optimax Slurping Goodness in Carbon Black

2013 SDV6 HSE Black Edition- Orkney Grey with Ebony & Ivory. LR Facelift RAI, Genuine G4 Expedition Rack, 4x Warn SBD-160 Spotlights, Warn 9.5XPS Winch, Mantec Underbody Protection and Sump Guard, Full Easy Lift Suspension Module, LR Light Guards, Light Force HTX230 Hybrid spotlights, 18” Compomotive PD1881 on 265/65/18 BF Goodrich KO2, ARB fridge, TuffTrek awning 😎

I have been in contact with the above via AULRO . I have howber got the specs of the electrical system now so can move one re Battery options. M16 SVD8 ,4.4 HSE with a few extras, Sold R50 , Wife SQ5 , BMW R1200GSW.