Unfortunately, yes.

When an electric motor is working from batteries, it will run until the battery is "deep discharged". And rechargable batteries are usually ruined when discharged past some fairly high voltage.

However, there is a somewhat less expensive way to do this. Unfortunately, it'll probably run the motor a very long time. Let me illustrate with a story...

Long ago, my bunch of glider flyer buddies and I had just "discovered" slope flying. None of us had ever done it. We also discovered that long slope flights could be recognized for "reward". So a few of us tackled the problem of flying long flights with our existing equipment. All our TX/RXs back then ran on NiCd's that didn't have a lot of capacity. Most of our airplanes wouldn't fly longer than 3-4 hours and the transmitters wouldn't operate on their NiCds longer than a couple of hours. Everybody started looking for NiCds with lots greater capacity. All of them were huge and wouldn't fit where the original packs fit. It dawned on me that some of the cheaper TX/RX setups used AA flashlight batteries. And those suckers had lots more capacity than my AA size NiCds. On my first attempt, I flew about 3x's longer than the usual 3 hours. You're not going to want to fly a CL airplane until the flashlight batteries run down. Unless you're the Energizer Bunny.

When you run rechargable batteries until they're "out of gas", they're often ruined. There is a chance that the performance will have dropped enough that the airplane wasn't flying any more before the batteries are deep discharged, but are you willing to risk ruined batteries to find out?