Fiat Ducato 2008 130 multijet on Ace motorhome alternator problem. Battery warni g light flickering on off. Belt changed no change. Alternator charging battery ok. Any ideas told may be a fuse near the Battery???

Check the D+ connection on the alternator. The lamp has 12v supply to it and when the engine is not running an earth connection is provided via the alternator which operates the lamp. When the alternator is running then the earth is replaced by 12v so the lamp has 12v on each side and goes out.