2002 is300 issues

[ConnorGault245]

Hello all i bought an is300 a couple weeks back, always wanted one due to my nfs days haha anyways since driving it im starting to notice that there are afew issues such as the electronics. When driving and i have the radio on and when i do another command such as AC or indicating the speedo dims, radio cuts out for a second almost as if there isnt enough electricity for everything. 
 

on top of that when I accelerate it doesnt feel like it has as much power as it should my bmw before it was heavier, less bhp but felt soooo much faster. Id like to add i have no idea when it comes to cars i just like to drive and admire them, any help or advise would be great.

[messi]

It could be a weak Battery or maybe alternator issue