Even with the newest of batteries, you must still give them a 100% complete charge the first time. It may not require a full 24 hour period, but at least 12-14 hours (however 24 hours is recommended by most manufacturers). This is due to the chemicals in the battery and the reactions of those chemicals during their first charge. The initial charge will directly affect the capacity of the battery. Not fully charging the first time can lead to the battery prematurely going bad or giving less and less talk time/standby time.
From personal experience, I haven't noticed much of a decrease in battery life from a 12 hour charge vs a 24 hour charge. But batteries I have only given a 3 or 4 hour charge initially have had a 30-40% decrease in capacity over the course of about 6 months.