Prius battery won't trickle charge

i have that exact charger get the red on solidly that port is tricky to get tight on then move ground around till it sets the light on indicating charge unf. in most I do it all at battery . from front it usually heats up wires a bit. at battey no heat unless battey really bad

 

and im guessing you have no DVOM or test meter whats reading at battery if under 10 volts and nothing left on . time for new 12 V. if new return to store ..

 

If the battery is dead, don’t use a trickle charger. Get a real charger and fully charger it or take it to a parts store and ask them to charge it and load test it.

 

Try a different ground point for the black clamp, the inverter cover probably not the best ground. Maybe a body colored bolt just above the red clamp. Max charging current for Prius 12 volt battery is 4.2A The 3 amp Schumacher charger is sufficient, just may take a couple more hours to charge.