Thanks Struth – I had noticed that on short journeys – less than 8 miles – it would only be towards the end that battery usage would tick up to late 4’s or 5 – I almost always have music on from iPhone connected to usb – hence my wondering as to where it was drawing current for phone and speakers.
So it could be main battery charging smaller battery whilst driving – so coming from main battery via 12 volt battery – I will make one or two journeys in silence with iPhone in my pocket to satisfy my curiosity. ??