Modern batteries have a habit these days of going "fine, fine,fine, nowt"

Been finding the 2CV's engine is a bit choppy on the tick over. Just filmed a very short video which is here... https://www.youtube.com/watch?v=rJxy0ef-YlI taken in the garage with the car facing out and the door open. Sounds a bit noisy, but I don't think there's a blowing exhaust at the moment, though I may well be wrong. I'm certainly not getting any fumes coming into the cabin, and the exhaust tailpipe note sounds quite healthy if you disregard the choppiness.

Batteries get damaged when emptied to much, with a start battery more than 20% could already be to much

Thought of today:- The bloke who designed the manifold/exhaust on the 2CV. I hope he's burning in the hottest part of Hell.

It's hard to disagree with that.....

Explain, svp?
Details of an alternative or improved arrangement would earn credibility...

Suspect it might be due to that unerring habit of not seating properly if the heads aren't loose and blowing gaskets.....

I would think the reason for those problems are lack of knowledge by the mechanic, not poor design from the designer. There's a big difference

Nope. It's the complication of multiple joints (manifold to heat exchanger to crossbox on both sides of the engine) and having to ensure all joints are tight. The problem comes with getting it nice and tight on one side, only to find a gap big enough to sail an oil tanker through on the other side. Then finding the clamps aren't wide enough to clamp around both flared ends of adjoining pipes. A bloody nightmare! Would be much easier to just have twin exhausts and do away with that bloody crossbox.

Ahh! The proverbial shite exhaust clamps.....the Burton ones are well worth the investment and will clamp much better than the original designs - I believe single pipes down each size don't give enough back pressure and reduce effective bhp - the design of the exhaust is quite complex and gives similar exhaust gas lengths so as to balance the pressures from cylinder to cylinder - if you look at racers exhaust design with no cross box it involves quite exotic pipework to give similar exhaust tracts....