What type of car battery?

[JTaylor2005]

I have been having sluggish starts and the dashboard needle problem some people get. I have cleaned all the earths etc and tbf looked through the receipts for the car and the battery is a good 5 years old. I will probably be getting a new one soon. What size are ours. I have seen on one website that it is 027.

Also what would people suggest? Some are very expensive. I am thinking probably a Bosch but I have seen new Duracell ones and they look good. I suppose just one with a good warranty would be good enough. 

Thanks