1. Lithium spares usually go in your carry-on
Most airlines and aviation authorities require spare lithium batteries to be in cabin baggage, not checked luggage, because they can catch fire in the hold.
2. Power banks have limits
Many airlines limit the size of power banks and may restrict how many you bring. The rating is usually printed on the bank in watt-hours (Wh).
3. Protect the terminals
Tape over the terminals of spare coin cells and 9-volt batteries, or keep them in their original packaging. Loose batteries touching keys or coins can short out.
4. Alkaline cells are simpler
Alkaline AA and AAA cells are generally allowed in checked or carry-on luggage. Rules vary by country and airline, so check before you fly.