What does red blinking mean?
The red light should indicate that the unit is charging. If the green light never illuminates, that could indicate an issue either within the batteries or within the charger. In that case, we would recommend bringing the batteries to a local auto-parts store such as Autozone, Walmart Automotive Center, or Batteries Plus and requesting a Load Test. A Load Test result of less than 70% would indicate an issue with the batteries, anything higher would indicate the batteries are fine and the issue could lie within the charger itself.