Drone batteries are an expensive and critical part of the aircraft. Learning to look after them can help save you money and make your flights safer. Unfortunately DJI guidance is a little sparse (see the official DJI "manual" by clicking on the image below)
I’ve spent some time reading up on how to look after my Phantom 4 batteries, and the results of my research are here:
Lithium Polymer (aka “Lipo”) batteries can be dangerous if overcharged or misused so check the battery for swelling, bloating or cracking before and after charging/flying. If it shows any signs of damage, dispose of it immediately as damaged Lipos can become unstable and explode. It’s unlikely, but not worth the risk.
When charging, place it in a non-flammable “Lipo bag” – these are designed to reduce the risk of damage or fire in the event of the battery exploding – and never leave it unattended.
Store your battery in the Lipo bag and at room temperature (5C to 25C)
If you’re not flying for a few days, store your battery at around 50% charged (never fully charged or completely exhausted)
Never discharge the battery completely as this will damage the battery and possibly render it useless. Land your drone with about 20-25% of battery left to help reduce this risk.
After a flight, wait for the battery to cool before re-charging.
Only charge your battery to 100%, the the day before you fly.
Calibration: There is a lot of conflicting advice on whether you should or shouldn’t periodically (after 20 flights) discharge the battery to below 8% and then recharge it. The idea is that this recalibrates circuitry on the battery which works out how much % of a charge is left and helps it accurately reflect the charge stored in the battery. My view is don’t do this - the risk of damaging the battery by over-discharging it, outweighs the possible advantage.
Automatic discharge: Using the DJI Go App, you can set the batteries to automatically start discharging after a set number of days. Again there’s a lot of conflicting advice, but my view is that this should be set to 3 days.
So in summary, aim to land your drone with about 20-25% of battery left, store the battery at around 50% charge and only charge it to 100% the day before you fly. Your mileage may vary of course, but this is how I personally look after my Lipo batteries.