Prius only Starting after Jump

Its possible that you have some kind of leak that discharges the battery when the car is off. Maybe one of the interior lights is turned "ON" permanently?
Another possibility would be oxidized/corroded clamps on battery (clamps that connect to battery posts) or they are not tightened .

- Alex

 

If it will start with a jump the problem is with the new 12 volt battery or the cables it hooks up to. Charge and test the 12 volt battery and check the cables including the ground where it attaches to the body.

 

Some have reported that their new battery arrived in a discharged state, so it always best to check the condition before installing.

 

You can't see a bad connection. As stated above, the ground connection to the chassis needs to be clean and tight. Measure the voltage at the jump point under the hood with a voltmeter. You should see the same as when testing at the battery itself, with no loads.

There has been one post saying that the connections from the rear to the front of the car were faulty. I think it was John BritPrius that pointed out they were aluminum wires, and could become corroded and faulty.

 

This is a repeat of advice that you've already been given:

Check the mechanical tightness of the positive battery cable as well as the negative battery cable both at the battery and at the body of the car.

Use a digital multimeter to measure battery voltage at the battery terminals, and also at the dedicated positive jumpstart terminal in the main relay/fuse box near the inverter. When the car is IG-OFF and after surface charge has dissipated, the voltage of a fully-charged 12V AGM battery should be ~12.9V. There should be little or no difference in voltage when measured at the two measurement locations.

How much current will your battery tender produce? A wall-wart tender is useful for keeping batteries at a full charge but not so great in bringing a depleted battery up since the current output typically is 1A or thereabouts.

If you can't find a problem given the above, the next step would be to measure quiescent current draw when the car is IG-OFF, the doors and hatch are closed and locked, and the fob (if Smart-equipped) at least 15 feet away from the car. A 2G should show around 0.02A current draw (20 mA or so) after the ECUs settle down.

 

Trace the negative cable to the point where it attaches to the body. Use a 10 mm socket to tighten the bolt, as needed.

 

You should have had to access this already to install the battery correctly. Usually when removing the prius battery you remove the positive at the battery terminal and the negative at the body connection.

 

You mentioned before that it will only start if jumped. Is that still the case or has it progressed to not starting at all?

 

Please use your digital multimeter to measure battery voltage at the battery, and also at the main relay/fuse box near the inverter, at the dedicated jumpstart terminal. Report your measurements at both locations.

When you jumpstart the Prius, exactly where do you apply the jumper cables?

 

And then it starts and drives normally?

 

When you measure the voltage at the back are you measuring from both battery terminals or from the positive terminal to a bolt on the bodywork?
Something for you to try that may point to the fault directly. Connect one jumper lead to the jump point under the hood, join the other end to your other jump lead (making one long jump lead) do not let this joint touch the car , now join the end of the second jump lead to the positive + red battery terminal. Does the car start?

John (Britprius)

 

There is only two reasonable reasons for this, number one is there is a fuse link in the positive terminal at the battery. Check with your volt meter to see if there is 12 volts at the point where the cable joins the terminal, if there is 12 volts there the cable has corroded through at some point. Many are made of aluminium. You can either trace where it is broken (sometimes not far under the front fusebox) or replace the cable complete with some copper cable from your electrical store. Or more expensive replace with the Toyota part (no advantage in this). Any further help just ask.

John (Britprius)

 

Good to see that you are very close to a solution. There should be a problem somewhere at the 12V positive battery terminal, 120A MAIN fuse, or cable.