On one of the RC forums I read about a break-in procedure I recently tried with a number of new batteries. I lost the link but I think I can essentially remember the procedure:
1. Fully charge the battery at no more than 1S. Let the battery sit overnight, or at least for about 8 hours if possible.
2. Discharge the battery to a safe storage level, roughly 3.80V per cell. Discharge slowly; I think I was discharging at less than 1S; for example, I was discharging at .2A on a 3300mAh pack. Let sit overnight, or about 8 hours at minimum.
3. Repeat step 1.
4. Discharge the battery as in step 2, except discharge to 3.50V per cell. Let sit overnight, or about 8 hours at minimum.
5. Repeat step 1.
6. Discharge each cell close to completely discharged. My charger won't let any cell get below 3.30V per cell, even though full discharge would be about 3.20V per cell. Check your charger as you may be able to limit the minimum voltage per cell. You need to carefully watch the battery as it gets close to full discharge just to make sure. Let sit overnight, or about 8 hours at minimum.
7. Recharge to storage voltage of about 3.80V per cell, and leave the pack alone until you're ready to fly. You can recharge at 1S this time.
The thought process around this break-in procedure is that it allows the chemistry of each battery to better adapt to being charged and discharged, and slightly reduces the resistance of the battery, which should reduce the heat generated during a discharge while flying.
This process is somewhat time consuming. I work at home, and just followed the process each day, keeping an eye on the batteries during each cycle. I use a Horizon Ultra P4 charger, charging and discharging four cells at a time.
I've never had any batteries swell up. I keep my batteries at room temperature in the off-season, and never charge them above 1S. Overly rapid charging and over discharging of batteries are the main causes of swelling of the packs.
I saw other replies to this string indicating that folks charge the packs the night before flying, which I also do and have had few problems with. If you can "top off" the batteries in the morning, that is also a good idea.
Hope this is helpful!
Rick