Ok, so If your Macbook trackpad is not working, the last thing you suspect might be your battery. Yep, this is happening to me right now. New book same problem. You'll find dozens of blog posts about deleting files, upgrading and downgrading but what it comes down to is the hardware.
What happen was I left the laptop sitting on the bed for a time. The battery then the casing got hot and started warping.
The thing is that for some reason I just ignored the swollen battery even though it felt odd. Once in a while would lift the laptop by the corner where the battery is located. The trackpad would instanly start malfunctioning. Then I tried an external mouse. This worked for a while but then the pressure on the trackpad overrided it after a while.
At every developer meeting there is always a conversation about Macs and why developers prefer them. I have to say now this is my second Macbook and it's going to be my last. Sitting on the desk a Macbook is a beautiful thing. But everytime I use it as a portable things like batteries, keyboards, casings and screens start falling apart. Nevermind that Apple replaces things for free. At the Macbooks price point I want quality even after the warranty. Otherwise I think it's better to just by a new Windows PC every year.