Battery issues?

I have a 1st gen ipod touch which i haven't been using much recently. I have just started using it again and the battery has been acting a bit strange. It will drain, and then when i plug it in to charge it will show 3 quarters full almost immediately. Why is it doing this? Is the battery on it's way out?

Yesterday it was on 3 quarters charge, and then all of a sudden went down to 20%. Today after a few hours charge it lasted for 8 hours playing music.

Thanks for the help.

 

Yeah it is pretty old, 4 years or so. I'm actually thinking of sending it to a company to get the battery replaced, it only costs £40, the reason i'm not getting the 5th gen is I am going to South East Asia for 6 months and don't really want to take new tech with me in case it gets stolen.

 

Well i did a full charge and it ran for 9 hours playing music before it died (wifi on, lots of 320kbps songs, screen off, no headphones plugged in), which isn't too bad. However, because it is so old, i'm wondering whether it would just be worth it to get a new battery? Would i see a difference, or am i just as likely to get 9 hours playing music with a new battery?

 

I don't think it has a speaker (at least mine doesn't). If i get a new battery and it lasts 15+ hours i would probably get one, but not if it only gives me a few more hours. I just don't want it to die on me when i go travelling as then i won't have any music

Edit - update:

Just gave it another full charge, and this time turned wifi off. Very very strange, but it drains much faster with the wifi OFF. I have never come across this before. How on earth would having the wifi off drain the battery?