Hi
The alternator fitted to my 04 2.0Hdi Citroen Relay is a 150amp and I have a standard Split Charger Relay bought at the local motor factors for £9.00.
It's wired up the the alternator charge wire to power the relay and the battery to the 2nd leisure battery via a 15amp fuse. Using the alternator warning lamp lead, you ensure that your battery is charged automatically the moment the engine is running, but the battery's are keep 'separate' at all other times. This is the same way caravaners do it.
No problems to report as yet.
It's exactly the same unit that I removed from my 1.9D which had a 95amp alternator and it worked perfectly in that van for a year and a half.
As nearly all of my customers are within a 6 mile radius from home, the van doesn't do enough mileage to keep the leisure battery fully charged (although the van battery is always fully charged) so I top it up on a weekend with a separate 6amp battery charger.
Spruce