I advise doing the mathmatics for the problem rather than assuming they will be fine.

The basic way to think about it, batteries capacity is given in Amps per hour (Ah). In other words if a battery is sold as 2Ah then it will provide 2 amps of current for a solid hour (at least in theory it will). Now we can use this to work out if the battery will last in battle. A battle is around 3 minutes long. That is 1/20th of an hour so the 2Ah battery will be able to supply 40amps for that battle (again in theory, it does depend on the batteries internal chemistry if it can make this figure). Good batteries should always be able to tell you their constant discharge rate and their short term discharge rate. The second being used when a large amount of current is required at a motors start up. With regards to a drill motor, I'd say a good average for the time in battle will be of the order of around 10 to 15amps average over the entire battle. Lets say because you are using 4 drill motors each motor needs 10Amps average to push featherweights around for a full 3 minutes. So your drive will require 40amps continuously over the entire battle. You can then use this figure to see if your battery will last the full time.

There are always assumptions in this calculation (there always are in any engineering question) but the key is to reduce their impact on the real world solution. I therefore always like to over engineer robots, throw in more capacity than is required and beef things up. Of course this comes with weight problems but its all part of the bigger problem of coming up with a reliable machine.