This Niski poziom baterii icon is made in Material Design style developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 4,300 icons, all in the same style and quality.
This shape is basically a rectangle with rounded edges. On the right center of the shape, is what looks like the right side of a regular rectangle protruding outwards. On the inside are two vertical lines on the left.