So, yesterday I was in a greenlaning event, nothing major and i do not think I hit anything, but I did spend a good 4 hours on mainly first and second gears. An error came up which brought the car to reduced performance. Using torque i quickly cleared the error and the car was fine for the rest of the event.

Today i went to start and at first it did not start and when it did start, i had a big list of problems and faults, including abs, airbags, hdc, traction, electric windows, parking sensors... Basically everything.

I think the problem is the battery... What do you think?

Certainly sounds like battery voltage - could be the leads have been been jolted loose, low battery )get it tested professionally under load) OR the infamous earth strap problem. No Longer the owner of a 2013MY Fuji White GS

"Fiat Lux" a philosophy not a car

What about the 'earth strap' issue? Does adding an earth strap solve the problem, and can i just add one 'for good measure'?

Search the forum - there are loads of posts and helpful tips about it No Longer the owner of a 2013MY Fuji White GS

"Fiat Lux" a philosophy not a car

took it to a land rover specialist, said that battery should be fine since it is at 85% (12.19V switched off) but it needs a good charge. For me it just means it needs to be replaced if I dont want any trouble. He also mentioned that the alternator is slightly over charging the battery, at 14.79V, but that could also be the alternator trying to balance things out with the worn out battery. Does that make sense?

If you are still experiencing the symptoms after a full battery charge then you should try a "hard reset" and/or fit the extra earth strap - both are explained fully in earlier posts No Longer the owner of a 2013MY Fuji White GS

"Fiat Lux" a philosophy not a car

fitted new battery and so far no errors and looks good, but I noticed that the alternator is giving weird numbers - not sure if it is normal. For example on idle it is sometimes off (voltage at battery is 12.5V) but goes up to 14.5V if I put some stress on the battery (like opening a door). Is this normal or a case where the alternator is dying?

I think that is normal, on idling and battery is full it stops charging, soon some current being drawn it starts in high voltage but will drop down eventually depending the rate of the current being used. Don't take my words for it though

I also think it is normal. I connected using torque app to monitor the voltage during the morning rush hour. I noticed the voltage was between 12.9V and 15.1V.

I am worried that the 15.1V which was not just a peak but stayed like that for a few minutes, may be too high for the battery and will eventually ruin it.