One way I accomplished this is using this block from sparkfun: https://www.sparkfun.com/products/13034?gclid=CLGS76bG9sYCFYQ8aQodypgIMA
I hacked something together by flipping the battery pins (and thermistor pins) on the breakout board to the other side, then removing the power button. So you can mount the sparkfun block to the breakout board and then the edison to the sparkfun block. Alternatively you can just use a level shifter for i2c. There are various posts on this forum about it, but basically the edison uses 1.8V for i2c instead of 3.3v like the rpi. I think the MCP ADC chip you mentioned uses a range, but ~3v being on the minimum required voltage.
Once you get the level shifting working for i2c, then using an external ADC has worked well for us!