Maybe letting the drone go carrying every energy boost bought by default. Then, you could add 1 energy from reserve at any moment except when it runs out of it. That way there would be more strategy to it and the punishment of losing the drone would feel deserved either for being too greedy by trusting too much in luck or stingy by hoarding energy, or even for being short-sighted by not buying enough. It may be necessary to playtest that system a little though, maybe reducing the amount of energy of every energy boost you buy, or perhaps increasing the price, IDK.
Just a suggestion. Anything else is great so far IMO. Good luck with this one, dev!