Not charging

I drove my car to the store and upon exiting it wouldn't start. I checked the battery voltage and it was down to 9.5 volts. I was working under the hood yesterday and my wrench made contact between the alternator housing and firewall and there was a spark, it did not touch the alternator wire or anywhere near so I'm not sure why it sparked? But now it doesn't seem to b charging.

Additional information:

I have an aftermarket stereo and sub and multiple maps. I have a second battery wired to the trunk for the audio system. Took both batteries out of car and charged overnight and topped up with water. Will be going back to drive car home in a few but unsure what to test from here.