Disco 3 (LR3) Is My Battery Dead...?

I left my 2006 LR3 diesel Discovery over the winter here in the UK for about six months while abroad. Now back and trying to get the Landy up and running again. I left a battery charger with the parents to charge the battery every couple of weeks....but....looks like the battery has been damaged. (Sulfation)
After charging, the battery reads 11.8 Volts.......while running 15.1 Volts (good alternator!) After a mile's test drive....the battery is 12.1 Volts. Even after charging for hours...the battery doesn't go above 12.4 Volts.
While test driving, after half a mile a brake kicks in and all sorts of lights appear on the dash. Including the brake light under the oil gage. It also seems to think the hood is open sometimes.
So.....new battery? Replace brake light switch? Help and advice appreciated..!!

IMO that battery is FUBAR... if the battery was charged while it was connected to the vehicle that's one evidence that it's the wrong way to do that

It was actually a BuddyGo battery maintainer/charger. According to the charger/maintainer instructions it says that it can be maintained and charged while installed. If it were just a charger.......of course I'd remove the battery. I'm 90% sure the battery is bad. Just weird that the brake would come on as driving. It was pretty instant and felt like maybe only one wheel. Can the vehicle behave like that with a bad battery? Or....would this be the brake light switch misbehaving?

Probably handbrake electronic control messing around, having been unused for six months

freelance said:

Probably handbrake electronic control messing around, having been unused for six months

Click to expand...

and would a very weak battery, whilst driving, make the parking brake misbehave..?

Weak battery on D3 causes all sorts of errors

Halfords Yuasa 019, find someone with a trade card for a sensible price.