if you flash a lot it may be a hassle to do this but from reading up on numerous threads on roms, kernels and battery charge on the XDA, I find it helpful and get best results from calibrating after flashing a new rom or kernel. a few charge cycles work best.
there are many different but similar methods here are a few.
These methods are meant to help increase battery life. I take no responsibility if it doesn't work or your phone explodes, you get eaten by aliens, etc.
Method #1:
1) Plug in and charge until LED turns green.
2) Unplug for a few minutes, then plug again until green.
3) Check battery stats to verify it says that the battery is full (while still plugged in).
4) Reboot into recovery and wipe battery stats.
5) Boot fully into phone, then unplug.
6) Use phone until it shuts itself off.
7) Turn on again and again while taking battery in and out of phone. Keep turning on until it won't even power up for a second.
8) Keep phone plugged in until fully charged (LED turns green).
9) Turn on and use normally for a few charge cycles.
Method #2:
1) Turn your device ON and charge the device for 8 hours or more.
2) Unplug the device, turn the phone OFF and charge for 1 hour.
3) Unplug the device and turn ON.
4) Wait 2 minutes, turn OFF, and charge for another hour. "Your battery life should almost double."
Method #3:
1) With the phone on, fully charge the battery (until the LED turns green).
2) Once the LED turns green, unplug the charger until the LED goes off.
3) After the LED goes off, plug the charger back in.
4) When the LED turns green, power off the phone.
5) With the phone fully powered off, unplug the charger.
6) Wait until the LED goes off, then plug the charger back in until the LED turns green.
7) When it turns green, unplug the charger again and go to step 5.
8) Repeat steps 5 through 7 ten times. This may take anywhere from 30 seconds to 30 minutes per cycle. It typically takes only about 1 minute, though.
9) Reboot into recovery and wipe battery stats.
10) Reboot and enjoy!