mobile

So I've been noticing that my M7's battery drains a good bit faster than it used to. I've been thinking about opening it up and putting a new one in, but I'd like to find one that has a higher capacity than the 2300mah standard one. I have searched on amazon and googled it but I can't find anything larger than the stock charge capacity. Has anybody seen one or know where something like that can be bought from? I did find that HTC actually makes a much higher capacity(3300 mah) for the M8(2600) that fits inside the phone, so that got me hoping that something like it exists for the M7.