In the Green Lantern: The Animated Series pilot, it's shown that the Green Lantern Interceptor is powered by a Power Battery. Would Green Lantern Rings be able to normally recharge off that battery? The regular batteries the Green Lanterns have are much smaller than the one that powers the ship. When Hal used it to try and recharge his ring in an emergency, there were some side-effects.
I don't remember if it was in the original pilot, or added on when they adapted it for a 1/2 hour stand-alone for the series, but after that, he wakes up in the ship and Kilowog says something to the effect of, "You're lucky you didn't lose your arm by recharging from the engine." (Forgot the quote word for word, but there was a reference to losing his arm and recharging from the engine or ship's battery.)
The implication being that the ship's battery is a much more powerful source of energy than their lanterns, so recharging through them is kind of like sticking your fingers into a 240V outlet -- the extra power is going to be tough to handle. Which means Hal is lucky to have done that without being knocked out or knocked halfway across the planet (or in having his arm fried or destroyed).