A hard clear battery case that holds either 2x 26650 or 4x 18650 batteries.
A must-have if you use external batteries that are often out of your device for charging.
Always store batteries in a suitable battery case when not in use.
Never put batteries in your pocket or handbag loose, other objects like keys or coins could cause the battery to explode.
Make sure your battery case is in good condition and can keep the batteries secure.