I have a problem with my Nissan Qashqai, its a late 2010 so its a facelift model. The lights flicker when I am driving, when im parked, basically all the time, my windows roll down slowly, some electronics have started dying, like my alarm system, and the latest is my rear & side mirror heaters. Any idea why is this happening ? its a 1.5 dci, original battery, and the voltage fluctuates, the flickering gets worse if ac is on, heated seats, or phone charger. I can turn everything off but it still continues to flicker.
You pretty much hit the nail on the head with "original battery". A decent battery will last 3-5 years before it starts to fail/cause issues, so first port of call will be to a store to get a new like-for-like battery. Beyond that, your alternator might be failing but you should get a new battery anyway.
Your symptoms sound much more like a problem with the alternator/charging system. If the car is running, the charging system should be taking most of the load even if the battery is no good, and it generally sounds like yours is having trouble keeping up with the normal demands of the vehicle. Definitely get your alternator tested. (I have personally been in a couple of vehicles when the alternator died, and what your car is doing sounds a lot like that. lights get dim, radio fails, basically all electrics start to go out and then the engine stops)
Also note your battery may still be bad, and a bad alternator can wreck a good battery over time. This also means replacing your battery before having the charging system investigated could be a waste of money, so I would hold off on that till everything else is cleared up first.