Alternator help!!

The other day the battery light came on in my car, I drove it for a day then went I came out of my friends house after only being 15 mins the car wouldn't start. Its wasn't the usual flat battery sound it was just ... 'tick tick, ticking when turning the key.

I left it there all day and went back on the evening to tow and the car started but as if it was a low battery. Drove it home and when I was around the corner from my house the downhill decent, TC and ABS light all came on.

Then when I turned it off and tried to restart it, the ticking when turning the key returned, so we connected it to jump leads and it started straight away.

So after my uncle looked at the car he said it was the alternator, so I went to GSF car parts to buy another and the assistant asked if I would like 100w or 150w, so I opted for the 100w.

The question I would like some advice/help with is, when we removed the old alternator is was 115w. The one I have is 100w. Is this ok to fix or should I get the 150w?

Thank you for all answers in advance!!
Miss Redman.

If the factory have fitted a 150 then that means the car will mead 150 amps to recharge the bat when you have every thing on best to change the bat to

Its fitted with 115, I bought 100 but the only options to buy are 100, or 150.

My 03 TD4 with air con has a 150amp one, and with everything running, heated screens front and rear, headlights, max fan, air con running, it needs it to continue trickle charging

would the 150 amp fit ?

Well mine fitted and that's what came off, I guess it depends what engine and auxiliaries you have running/under there