I sacked up and bought a new battery, actually a step down from the Interstate H6 (Powervolt) . It was a tad too big but I readjusted some wires and it dropped right in.

Also picked up a new ground/neg terminal and mounted it. Cleaned the pos off with a toothbrush.

Connected it up, dropped the RCM down (didn't bother soldering as my mechanic warned against it unless last resort). Turned the key and not even half a crank it started right up. Sweet angel music to my ears

Drinking a mojito now celebrating. What a huge relief off my chest, for only $85 total. Thank you all for the help. As for the RCM, I'll keep an eye on it but for now it seems to be good to go.

Thank you all.