Check out mooches tables and test results for all the info, but for 75 w on the solo, you'll want a 25A battery, so a vtc5A or Molicel 4p2A, or anything else mooch recommends in that range.
When using cells in the Aegis X, you should only use cells that HAVE NOT been used in the solo,. This is known as battery marriage. So, buy three or four sets of batteries, and use them in sets until one dies.