Tips to properly transport spare lithium batteries:

Pack spare batteries in carry-on baggage.
Keep spare batteries in the original retail packaging to prevent unintentional activation or short-circuiting.
If original packaging is not available, effectively insulate battery terminals by isolating spare batteries from contact with other batteries and/or metal.
Specifically, place each battery in its own protective case, plastic bag or package, or place tape across the battery's contacts to isolate terminals.
Take steps to prevent crushing, puncturing, or putting a high degree of pressure on the battery, as this can cause an internal short circuit, resulting in overheating.