Why is my itouch battery dying so fast?

Now I've had this itouch for 1 Year and 4th months. (it's a 32gb 4th gen, iOS 6.1.3 and was new when I bought it.)

99% of the time I've had my itouch on the lowest brightness setting. (if there was a lower one I'd have it on that because I find the lowest setting too bright at times.) The only time I really need to have it on 25%-35% brightness is when I'm outside in the sun, or when showing other people stuff on it, but that isn't very often.

Now I can recall in the past my itouch lasting pretty darn close to all day long on days I was using it pretty much all day long. (so on days I wasn't using it all day long, my itouch could last up to a week on a single charge.)
If it was losing it's charge eventually it was something I didn't notice at all.

I almost never let my battery die completely since I heard that's bad. (It's something that only happen like 3-5 times?)

I usually do charge it completely except on days I'm impatient, but there's only a few times I've let it charge over night. (Since I heard overcharging is bad I did my best to avoid it.)

I recently took somewhat of a break from my itouch for the past month or so? I'd use it maybe every other day but I'd only use it at most 20 minutes?
And now I began to want to use it more regularly, and then noticed....I could actually see the battery icon change every time I went to look at it. (which is veryyyy unusual and never happen before.) and when it reached the approx. 80% mark, I noted the time down mentally, and found out it only lasted 2 hours.

So next day I actually go writing down everything I do in a memo pad, and switch between it, applications, and a battery app that gives me estimations.

(I actually let the itouch die completely yesterday on purpose yesterday because I heard that would help calibrate it....but I probably did it wrong, as I only charged it to 70% the next day because it was too close to bedtime and I needed my sleep timer.)

The space separates nights. (All of these are in AM the only one in PM is "2:30 died within a minute of use")

I'll test out how long it stays on after a full charge.... but for day two should my battery really go from 70% to 45% within what 13 minutes? (but maybe this could be a bad outcome from letting the battery die but not fully charging it? But why would it do so much damage to the time so fast?)

And for day 1 should the numbers really jump all around like that?

And isn't it weird how the first night I ran the sleep app I only had 10% battery power but my itouch lasted for a minute after use, but next day I run it battery is at 45% and like within 5 seconds of turning my itouch on next day it dies.

Do the batteries typically lose their charge capacity this quickly on lowest brightness?

Is this just really normal for an itouch not even 2 years old? (almost seems ridiculous to me if it is :/)