Adding a 12 volt to the six 8volt pack

[jonequest]

I am getting a new 72 volt Alltrax SPM72400 controller tomorrow so of course I am itching to go a little faster. I currently have 6 of the 8 volt GC8V red top batteries from US battery for my 48 volts and I have a 625 CC amp 12 volt deep cycle marine battery for my 12volt stuff. I was thinking of occasionally adding it to my pack in series to get me up to 60 volts. I could easily charge them seperately like I already am. Like I said this would be temporary. I know that it is not good practice to load different sized batteries in the same circuit. For example I know that if I put a little motorcycle or lawn mower battery in line with my big 8 volts it will likely have no lasting effect on speed and likely overload the little battery. BUT this battery is about as big as the 8 volts and is a pretty stout little battery, it says "625 Marine Cranking Amps" on it. I don't know if that is just BS marketing or there actually is a such thing as "Marine Cranking Amps" I am sure it just means 625CCA. It is way more than what is needed to run my headlight and radio, even with my subwoofer. Can anyone see any harm to run around the streets a little here and there with it hooked up? Not every day but whenever I need to roast one of the neighbors carts. I am already at about 27 mph with 48 volts and cannot wait to see what 60 would get me up to.