Replacement Battery for Ipod Touch 4th Generation?

Have ipod touch 32gb 4th generation. Bought it in late 2010. At first the battery life was decent. Now... it seems like after a full charge... after 1 hour of usuage... the battery runs out. This is with wifi turned on of course and when browsing online. I don't use the itouch unless i use the wifi so theres no point of me using it without it on. And yes i know wifi uses lot of battery life.

Does this mean my itouch is running out of battery? Can i buy a new battery for it? If so how much? Thing is i know i cant install the battery myself and would need someone to do it. Anyone know the total cost of this? How much is the battery and the service? Are there some batteries that last longer than others? Don't want a cheap battery. Is there one that last 3-4 hours with wifi on? Im in montreal can someone tell me where i can go? I know i can go apple canada but is there any place that charge less?

Im curious how long does your itouch 4th genration itouch last for with wifi on and using it constantly? I recalled back when it got it...i think it was 2-3 hours? I know if you just listen to music... i could get 4-5 hours easily. now im not sure b/c i dont use it for music.

Got another question. How many different types of batteries are there? Would it be possible to buy the battery with the longest battery life compared to the regular one? Or are all battery replacements the same for the ipod touch?