Replace the battery or the phone?

So - long car ride - 'plug in the phone, dear, would ya'.

The phone is plugged in with a good cord to a questionable unbranded USB - Car adapter. I didn't know it wasn't going into my power brick....but no crying over spilt milk.

The adapter had a bit of an explosion, just a pop and a bit of smoke. My phone seemed fine, no immediate reaction. It lasts the rest of the day and I plug it in at night to the wall. I noticed in the morning that it hadn't charged. We theorized that maybe the cord had been affected by the little blow up.

I had it off for an hour or so still trying to charge and when I pulled it back up I noticed battery life was going down 1% a second. Thought I'd restart it, maybe it wasn't recognizing the charge, but it didn't have enough juice to kick back on.

I did later try another cord with no luck. To reiterate, the phone seemed to function perfectly well - other than charging capabilities - for probably the next 12 hours that it had a charge. At first if I plugged it into a power brick the light on the brick would come on, but now not even that much. I also left it on the wall today in (probably vain) hope, and the phone did get warm...but wouldn't turn on.

So my question is - is it likely only the battery that was affected, therefore able to be easily replaced for a relatively low price? Or should I just go for the new one?