A large-sized fire resistant bag with heavy duty stitching and a strong velcro flapped opening designed to reduce the risk of fire and injury in the event of battery failure during charging. Whilst the risk of failure of any battery is very low, and the following of basic battery safety (use only appropriate charger, do not use damaged batteries or chargers, charge only when in attendance, remove batteries from charger once charged, etc.) reduces this further, it is good practice to charge all devices within a charge safety bag. I personally use one and I highly recommend all customers to do the same.
Bag dimensions are 29cm x 23cm, manufactured by Efest, a well-regarded battery producer.