I notice my ex-ambo T5 has a Start Stop battery fitted as a start battery, in the engine bay. Varta brand, 70 AH. Advertising on the battery label says good for installations with lots of accessories. No auto stop/start in this vehicle like son's Golf so I'm thinking the battery was an ambo upgrade because they normally run lots of "stuff". Bloke doing my roadworthy to change rego confirmed VWs do not like anything other than VW approved batteries (Owner's manual has a warning against replacing battery with standard stuff).

There is a second battery installed under the passenger seat. I have not worked out all the wiring yet but a solenoid controlled by a switch on the dash parallels this second battery (AGM) with the start battery.

Any experience with VW battery requirements out there who might comment? I already have a LiFePo battery it install as a third, to run a fridge, and will be tapping a charge output from the current second battery to the Lithium battery.

Iza