yea you can other alts to fit, but most people have gone for bosch(?) alts, which are used in the bigger corsa's etc like the diesels. But ask austin etc about these, since i havnt done it yet, nor looked up the info.
However, you can get your alt upgraded though, if you cant find/fit a bigger alt than what ya go :)

r there aftermarket alts u can buy then?

i bought the new battery and cause it is the high power one it did help stop the dimming of the headlights, and yes a cap will help sextons have some good offers on atm

upgrade your battery and alt, its the only way to overcome dimming lights etc. A cap might help, but its only like a little battery which stores some power when the amp demands its, like on heavy beats/bass etc However, its useless if you battery cant charge up quickly and provide the cap with more power to charge that up. Basically mate, just get a bigger battery and see if that works. If it doesnt, then your gonna need to change alts and once that works out ok then you can wack a cap in there for good measures :)

Ahh Halfords batts... I thought that there would be little point spending £120 on one of the Optima ones for such a small install - does it stop your lights form dimming when you get heavy bass, or would a good batt and a power cap be the way forward?

i got a 2 week old high power corsa b halford batt, asking £50 was £65 new 2 weeks ago and i wrote my car off 1 week after buying so i stole it back

cap would just use more power from battery when it charges. Just get an Exide Corsa turbo diesel battery.

surely you should just cap it? as you got 2 400W amps then it would be 0.5 farads for each 400W ? so you'd need a 1 farad cap and wudnt need another battery?

I think I need a new battery for when I do my install. Previously when I turned the power up to full all the lights dimmed, and sometimes my digi dash turned off! Thats cos my batts shagged anyway.

Whats the best batt to get - how much and where form? Also after that would a power cap do the system any good - Its got 2 400w JBL amps powering Sony 250w 6x9's and a 450w JBL Sub (RMS)...