Peugeot Partner bsi unit

I would be very grateful for some advice regarding my father's 2004 Peugeot partner Combi that I have been driving for the last few months please... While driving this vehicle after perhaps 5 minutes the battery light comes on followed by the engine management light and airbag light and if the headlights are on they dim and slowly stop working, the windscreen wipers also start on their own!
At this point all cluster guages loose power and flicker (Speedometer, rev counter, indicators and hazard lights stop working) the power steering drops out and it loses all acceleration then stall's. Trying to start the car seems to be almost like the battery is dead even though it's a brand new battery with just a click, so the only way is to jumpstart the car and this usually works then suddenly the car drives like there's been absolutely nothing wrong until the next time!! I have researched endlessly and the majority of the online advice listing all or some of these problems it could well be a fault with the bsi unit causing a permanent drain by not going into eco mode correctly. I have tried a both a bsi reset and removed the shunt fuse, waited and put back in but nothing is beneficial to rectifying the fault. As the bsi unit is connected to the immobiliser
it's almost like the car thinks that it thinks it has been stolen and everything stops working. I am using an original key and the car has been serviced as per Peugeot's service schedule. Many thanks in advance for any advice offered ?