Drone batteries are lithium polymer cells. They're safe enough when they're treated properly, and they're the part most often damaged by everyday habits rather than by accidents.
Storage
Store them at part charge rather than full or empty. Most manufacturers suggest somewhere around half charge for anything longer than a few days. Keep them cool and dry, out of direct sun and away from anything flammable.
Leaving batteries sitting fully charged for weeks between jobs is what causes most swelling and lost capacity. A lot of enterprise batteries will self-discharge to a storage level automatically after a set number of days, so leave that feature switched on.
Charging and flying
Let a battery cool down after a flight before you charge it, and use the charger that came with the aircraft. Don't fly one down to nothing, land on whatever reserve the aircraft tells you to. Keep firmware up to date as well, since battery management is handled in firmware on most enterprise platforms.
When to stop using one
Take a battery out of service and get in touch if it's swollen or misshapen, physically damaged or punctured, won't hold charge, gets unusually hot, or reports a cell error. Don't charge it and don't fly it.
Why you can't just post one
Lithium batteries are classed as dangerous goods. Couriers have their own rules on packaging, labelling and state of charge, and a damaged or swollen one is restricted further still.
So please don't post a battery to us without speaking to us first. Email [email protected] and we'll confirm how it needs packing and which carrier to use.
Warranty
Batteries are consumables. Capacity drops with use, and that's normal wear rather than a fault. A manufacturing defect is a different thing and is covered. Warranty periods and cycle limits vary between manufacturers, so tell us the model and we'll confirm what applies to yours.
If you think one is faulty, follow What happens after I report a fault? and include the serial number and cycle count.
Flying with them
Airlines want lithium batteries in cabin baggage rather than the hold, with the terminals protected against short circuit. Limits on size and quantity differ between airlines, so check with yours before you travel.