A battery's electrical connections (also called contacts or terminals,) must be protected from contact with metal or other batteries that may cause the battery to short-circuit. You can do this in many ways.
Keep batteries in their original packaging. This packaging is specifically designed to protect batteries in transportation, at the store, and in your home or worksite.
If original packaging is unavailable, tape over the electrical connections (contacts or terminals). Electrical tape is great for this job, but any adhesive tape not made of metallic material will do! Placing each battery in its own individual plastic bag will also isolate the battery's terminals.
Every rechargeable battery-powered device comes
with a charger that is right for that device. When you
travel, locate the charger that is compatible with the
device - don't mix and match!
Use protective packaging and safety measures such as
trigger locks to prevent inadvertant activation of power
tools, especially in checked baggage!