Code P1261 pd unit injector cylinder 1 (N240) regulation range exceeded

[dentist69]

Have just started to get this code this morning after trying to start car for first time in 2 days!
Bit of history first hopefully some guru on here will know what to do
Ok so for a few weeks I've suffering with intermittent misfiring at low revs (1.7k to 2.5/2.7k) in 2nd 3rd gears, usually when in queuing traffic that's doing a steady pace, around 16-25mph, soon as u give it some beans it would stop and run normal. You could never make it do it it just did it.
Also and in addition I've feared my battery has been threatening to die on me since the weather turned cold, struggling to crank and start but it's always fired eventually. I need to test it just to be sure its not the starter, i do get a rapid tick tick tick and the dash lights fade and go off so, well u know, more than certainly battery related
Anyhoo 3 days ago had a new crankshaft sensor fitted as it through up a fault with the sensor. Can't remember actual code now but defo wasn't this one, anyways took 3 days to do it lol.
And now I have this one. I've done some googling and it seems it could be anyone of 3 possibilities, the actual injector or the electricity supplying that injector. Whether a fraid wire or the fuel rail which has an electrical supply and is common to fail as sits under the rocker cover?

Could it be that code is being thrown up cos my battery is goosed or am I looking at 2 separate problems? If so what are most likely please? Already shelled out fortunes on it! Brakes tyres crank sensor etc