Sounds like some of the worst advice you've ever received unless you're waiting charge your LI batteries. The Lithium Ion battery is a great development but must be understood. If you charged it up and put it in your camera a month ago it's probably lost some charge in the interim. The best practice I've found is to charge batteries all the way up right after use and then recharge them to top them off shortly before you'll need them. That usually means overnight before a job.
The other part of my best practice is to have several spares on hand. Even if the battery gets below 50% of its charge you may find performance starts to disappoint. Specifically I find that my Wi Fi cards stop transmitting when the battery gets below 50% even if the camera seems to be operating normally.
I've also found that the batteries will gradually recharge less and less over time. You may find that a battery you've owned for over a year just won't charge to 100%.