Iphone turns itself off when it is 32% of battery

In Lately my iphone 4s has off alone when you get about 32% of battery.

And even he did not simply shut it off as if it had just the battery.

So I have to wait about 5mim and try to connect again, because before that he does not, because he thinks that the battery is over ..

Another solution I have to make him turn, is connected to the usb.

I even doing it on again, it switches itself off after a few seconds.

If I insist he even stays on, but when it lowers to about 22% it switches itself off again and so on until you fully deplete the battery following the indicator.

It would be possible problem of the firmware? have a possible solution? always liked this iphone, sorry that I can not afford to buy a 5S or 5C.

(sorry for bad english, I'm brazilian)