New battery, no battery light when starting

[onejon1]

Firstly I may be adding all these things together and this is skewing my view of what might be going on.

So in trying to fix my rear wiper, I created a short. The car wouldn’t start. RAC jump-started the car and said don’t turn the car off, go straight to buy a new battery, as this one is knackered. Got home with a new battery (without turning the car off) after stopping the car, it then proceeded to restart, it carried on doing so over the next week circa 40+ times. Wow, the battery must/might have survived the short.

Thursday 8/12/22 evening the car was still starting, however, overnight it went very cold and Friday morning there was snow, and the car did not start. I then changed my mind about the battery surviving and thought oh well maybe it didn’t, so I lobed on a new one and the car started. However, after driving for a while the battery light came on (first time that this has happened), and the windows, radio, and clock, which I think are on the same fuse, no longer worked. Put the multimeter on the battery while it was running it was only showing about 11.8 volt (possibly the alternator) took it to a garage they took off one of the battery terminals and the car carried on running. According to them, it is not the alternator, they don’t have a car spark so could not help me further.

Oh I forgot to mention, since the new battery was fitted, on first key click the various dashboard lights do their thing as usual, however, the battery light no longer comes on during this first click or indeed during the starting sequence.

After driving for a few minutes then the the battery light comes on.

Also, quite recently I had the cambelt, water pump & one of the tension bearing replaced. So no noises or slipping belt/wear and tear...

It's difficult to make sense of the fact that as soon as a brand new, correctly charged (tested in the shop)battery got fitted, that the battery light stopped illuminate in the starting sequence.

I’ve not had a chance to check the fuses, although the battery terminals appears good, but will double check, terminals and fuses etc. when it’s daylight.

Any thoughts, as always are welcome.

[liquidhandwash]

Is this the 306 HDI, the "mechanic" should be taken outside and beaten and shot for disconnecting the battery with the car running.
Most likely one thing has nothing to do with the other, I would be removing the alternator and strip it down, 90% sure the brushes and slip rings are worn out.
There are likely only a couple of wires running to the alternator the fat one goes to the battery easy to check if it's okay. the skinny one goes to the light on the dash. ground it out with the key on the light should come on. If its got more than one skinny wire they are current sensor wires you will have to get a wiring diagram to check which wire goes where.

[CitroJim]

Yes, disconnecting the battery on a running car is a very dangerous thing to do as much damage can result - looks like you've been lucky in that no apparent and immediately obvious harm has occurred...

Yes, do check the operation of the ignition warming light as LHW suggests above... It's critical all is well here as the bulb acts as a small resistor to provide the alternator's initial excitation current. If the bulb is blown or there's a wiring fault associated with it then it's a toss-up if the alternator will function on each start-up.

Much more likely the alternator is worn out as stated... And this current spate of cold in the UK is giving every car electrical system a good stress test and an intermittently charging alternator coupled with a partially discharged battery can pop up some surprisingly obscure and bizarre faults!