Yes, you should wait until the battery is completely discharged before you charge. You don't have to, but you should.
A rule in Electrical Engineering is that any Li-ion technology should recharge for 24 hrs. the first time.
Nikon's battery manual says 2 hours but also keep in mind Nikon makes money off of their battery sales.
When the charger indicates a full charge by a constant light this merely indicates that the battery will perform at a level that Nikon believes customers will find suitable. Suitable in terms of performance and charge time.
If you leave the battery in the charger while the light indicates a full charge the charger drops down into trickle mode. Power is being supplied but not at the starting rate. You can think of this as a cool down mode.
The most important thing to remember about Li-ion is that they will only hold a charge up to the charge they were first charged to. Wow! Try saying that 3 times fast.
Nikon technical reps recommend a full over the night charge (12 hrs.) for the first 3 charges. And they only recommend the charges after the battery has been completely discharged; not just when the battery indicator blinks and the shutter can not be shut.
This is why Li-ion batteries require the lengthy charge. “This initial trickle charge helps to redistribute the electrolyte to remedy dry spots on the separator that may appear when the electrolyte gravitates to the bottom of the cell during long storage. A slow charge also helps to bring all the individual cells within a battery pack up to an equal charge level because each cell may have self-discharged to different capacity levels during storage."
By the way. I don't find the charger to be too bulky and a hassle to carry.
If I were you I'd invest in a second battery. I found a seller on EBay who sold me a brand new EN-EL3 from Hong-Kong for $23.00. That included shipping. It took two weeks to get to me. But it worked just fine and was as advertised. Not to mention, the battery was made in Japan not in China like the battery that came with my kit.
I'm getting a D70 next month (from Hong Kong), that's for sure. I
was wondering whether I should get a second battery. I often travel
for 1-2 weeks. Is the charger too bulky to carry? If I take it with
me, perhaps that'd be enough and I don't need a second battery? Do
I have to wait until the battery to drain out before I recharge it?
Any advice will be appreciated.