would this be good for a rc10t4 and if so how long runtime?

If you put an 18.5V battery on a normal ESC that is designed for at most 8.4 V you are going to blow it up.

not to mention if he has the numbers typed correct that pack would be about 500.00 or more, 11,250Mah 18.5 volts WOW!!!! I would like to run that with my AXI!!! can you say 30or more pounds of thrust! and killer run time!

I converted a 1/8th scale Mugen MBXR-4 buggy to run with a pair of TP8000-3S4Ps in series with a total of 22.2 volts and 8000 mahs using a Schulze 40.160 ESC with a Hacker C50-10XL motor. So much power and torque it ripped the center diff out all the time. I used a Schulze 18.97 ESC first and it caught on fire from too much voltage.

This buggy would out run, out perform and out jump any gas buggy I have ever seen. It was way too much maintence, so I dismantled it and sold the buggy. I still have the ESC and motor that cost close to $800. The batteries cost a total of $400.