Hi Marcus / Joff
Im not an auto sparks but it looks like you should get some basic tests going, check for DC Volts at the battery terminals without car running 12V +

and with it running *13.8v + should be expected. Low or high volts at the battery will through up a fault code I think, probably doesn't matter when you test with paper clip test or peddle test but you should.
If battery voltage, without engine running is low, then Halfords or the like will "drop test" the battery for free normally, you just need the test to prove a point.
If the alternator is not putting out good volts then probably go down that route, always worth checking for loose or bad connections at both terminals and ground to car body.
There's probably a help chart or summat on here and I'm sure one of the other guys will through up a link?

Once some codes and volts are on here then the solutions will begin
Good luck
