Pleased I looked this up , just bought 16 plate Vivaro so will have to use the ordinary 12v charger each night until I can afford a b2b charger
The trouble is that a B2B charger may not be the complete answer to your leisure battery charging needs.
We are an industry that no one can fully cater for. Most of us use a lot of battery energy a day and do very little mileage. So completely recharging a battery at the end of the day on the drive home just isn't going to happen with short distances/time taken.
A motorhome will travel a long distance and then will probably connect to 'shore power' when they reach their destination. When they get back home the van will be plugged in and left until the following weekend for example. Its the same with a caravan. 'Wild camping' might deplete the batteries charge but again the battery will be put on charge when the owner returns home.
A lead acid battery takes time to recharge. Ideally we want a lithium ion battery as it will accept a faster charge. But the cons are that they cost a fortune and special precautions need to be considered when charging to protect the alternator against overheating. There are also charging issues when the battery is cold. You can't charge a Lithium ion battery when its below freezing.
Dazmond has two 110 amph leisure batteries running a diesel heater, electric hose reel and single pump. He has a B2B charger but still 'bench' charges his batteries every night.
The easiest way to check how the alternator behavours is to buy one of those voltage meters that plug into the cigarette lighter.
If there are times that the alternator produces 12.2 or slightly above volts then you have a smart alternator. If on deceleration your voltage jumps up to 15.0 - 17 volts then you have regenerative braking.
In either case you will need a B2b charger. With low voltage alternator output you will need a trigger wire to switch the B2B charger on. If your auxiliary charger socket switches off with the ignition then tapping into the feed at the socket will provide the power needed.
The downside is that if you need the ignition on to listen to your radio the B2B charger will be charging your leisure battery using the starter battery.