[spannerrash]

Beg, borrow, perhaps not steal a multimeter from someone, put it on volts and put the leads across the battery terminals. Start the car and check what voltage your alternator is putting out. Quick and easy test. Should be about 14.4V. If it's low, and I suspect it will be, I'd then repeat the test at the terminal box in the wheel arch but place the meter leads between the big battery cable and the chassis. You will have to probe around a bit on the battery cables because it is possible that a bad terminal box connection will give a poor result on the long cable going back to the battery and a good result on the shorter cable. This would actually be a good thing as it would indicate a bad connection in the box. An easy ish fix.

If all is well here then you need to be checking out the alternator. Could be poor connection's there or brushes worn-out.

Brushes are easy to replace, no soldering required but I am unsure if it can be done with the alternator on the car. Not sure if there is enough room to remove the rear cover and air duct to get access.