The usual amount of 1000 cycles is the official rating but in practice you'd probably get quite a few less. P.S. Typing this on an iPod Touch 5g, probably more than a year old (can't tell for sure as it's secondhand) battery lasts about 5 hours with games hogging most of the power.
It should be possible to use some of those external battery packs with the iPod to extend life. The iPhone 5s is about the same size so maybe battery cases made for them could work, I'm thinking about trying one out. Will let you know how it goes if I do try out.
That's RPM to you!!
