Have a look at this as a starting point: https://hobbyking.com/en_us/turnigy-...html?wrh_pdp=1
It's a 14.8v which is similar to your drill motors & should be OK for the actuator too. You probably could get away with a higher rated (5S) lipo too. Keep in mind that this particular model uses a XT60 connector so you will need to pick up a XT60 connector so you can plug it into the robot. You will also need a proper lipo charger.

There's a couple of threads on here about starting off with lipo's. I'd strongly recommend reading those first before committing to anything.