battery to battery or alternater to battery c

I met a chap with a Nuevo on a stellplatz at Zell on the Mosel a few years ago who had a Sterling unit fitted (can't remember the model) that kept the alternator charge rate high till the leisure battery was fully charged.  He was very happy with it and when I researched it on return home the spec looked good.

Not long after we got our current van with the sargent 325 fitted that works in the same way - its ok to charge with high voltages when the habitation electrics are disconnected from the leisure battery with the engine running.

Later Sargent units may also do the same so it would be worth chatting to Sargent before spending your money and you may also find that for modern Sargent systems that they will 'compete' with the Sterling, possibly disastrously - again talk to Sargent.

Personally I've found that an 80 - 100w solar panel connected via the sargent unit keeps both leisure and vehicle batteries well topped up.

Peter