So all you perspective photographers and just travelers alike, this comes from www.safetravel.dot.gov for public information I never new about it or the reasons. 

“The following rules apply to the spare lithium batteries you carry with you in case the battery in a device runs low: Spare batteries are the batteries you carry separately from the devices they power. When batteries are installed in a device, they are not considered spare batteries. You may not pack a spare lithium battery in your checked baggage. You may bring spare lithium batteries with you in carry-on baggage. Even though we recommend carrying your devices with you in carry-on baggage as well, if you must bring one in checked baggage, you may check it with the batteries installed.”

The following batteries used in Canon equipment are fine for air travel:
Equivalent lithium content of these batteries is not over 8g:
BP-85, BP-208, BP-208DG, BP-214, BP-218, BP-2L12, BP-2L13, BP-2L24H, BP-2L5, BP-308, BP-310, BP-315, BP-406, BP-407, BP-412, BP-422, BP-508, BP-511, BP-511A, BP-512, BP-514, BP-522, BP-535, BP-608, BP-617, BP-808, BP-809, BP-819, BP-915, BP-930, BP-945, BP-950G, BP-970G, LB-50, LB-51, LB-60, LP-E4, LP-E5, LP-E6, NB-1LH, NB-2L, NB-2L14, NB-2LH, NB-3L, NB-4L, NB-5L, NB-6L, NB-CP1L, NB-CP2, NB-ES1L
Lithium-metal batteries bundled with Canon products:
The Lithium content of these batteries is not over 2g:
LITHIUM 3V CR123A, LITHIUM 6V 2CR5, CR-2025, CR123A, CR1616 PIRO, CR1616, CR2, CR1220, CR1220-PM, CR2016, CR2032, CR2450