I wouldn't... if you short two batts together that don't have a fairly balanced charge on them, you're liable to fry them... the more highly charged batt will discharge into the other one at a very high current rate. You're liable to exceed the discharge rating of the higher charged batt, and certainly exceed the charge rate of the other. If you run those batts in parallel in your plane, then that's just like a 2P batt pack... the batts will be balanced, and shorting them together should be OK...