When I push the battery test button, it shows a low battery (models CJS 50, CJI 150, CJIC 250, CJIC 350, CJIC 550)

The battery meter is a bar graph.  If the battery is low, then only 1 or 2 of the LEDs will light up.

When the battery is full, all 4 LEDs will light up.  This is normal.

If only 1 or 2 LEDs illuminate, then try charging the jump starter overnight.