12V down to 6V - door ajar but dome lights off - what caused the drain?

I changed out the 12 volt battery....got good voltage to the relay box.....interior lights, head lights, flashers but the car still does not start? Any suggestions

 

Make a new thread and give the "back story". Describe the events surrounding it first failing, otherwise people will have no idea what's wrong.

 

One thing I have been wondering about, if I ever have to jumpstart my Prius:

Disconnect the negative terminal, jump the car using the positive terminal on the battery but using the disconnected negative CABLE (NOT the negative battery post) and after the car starts, then remove the jumper cables. leave the negative terminal disconnected and then once home, charge the battery using a battery charger, then reconnect the negative cable to the terminal AFTER the battery has been charged fully.

Any issues anyone sees with this, including whether it is safe to leave the negative terminal unconnected while the car is on?

 

It does not matter where you jump start the Prius, as long as you do not reverse the polarity of the connections.
The safest way is to connect the two positive ends of the jumper cables first making sure you have connected to the positive battery terminal on the downer car (or spare battery) then connect to the positive battery terminal or jump point on the Prius. The negative jump cable can be connected to the downer car (or spare battery) negative terminal or any clean metal part under the hood. Then the other end connected to the Prius negative battery terminal or again clean metal part or bolt.

Do not disconnect the negative battery terminal.

John (Britprius)

 

Sorry, I was not clear in the intent of my question earlier, which was to make sure the battery isn't fast-charged by the jumpstarting event or by the Prius charging system. To avoid this, I was wondering if it would be safe (for the Prius electronics, inverter, etc.) to take the battery totally out of the picture while jumpstarting the car as well as while I drive the car home. Then on reaching home, I can charge the battery using a slow charger and then reconnect the battery to the car?

 

I would not run the Prius without a battery connected. I know it will still run like this but have no idea how the 12 volt inverter (charging system) will react in that situation. It may give it's maximum output voltage (no idea how high that is) onto the 12 volt car system possibly causing bulb failures and even ECU problems, but doubt the voltage is that high.

John (Britprius)

 

". When I get some time I can open up the battery and look if much water is lost."
Remember that the Prius 12V is an AGM battery. There should not be any electrolyte above the plates. all electrolyre in an AGM battery is contained in the fluffy absorbant plate seperators, and you really cant check the amount in the seperators.

 

If OEM, time for a new battery. Old one is on its' last legs. My OEM was reading 9.5 v. Replacement took care of low voltage problem 6 - 8 months ago.

All is fine.

DBCassidy

 

That effect is the begining of the formation of a cell short. The sulfation bridges the plates, and shunts some of the charging current through itself, rather than the plate material. That means the cell with the short never gets charged up, and the water level stays high. Meanwhile, the other cells get more than enough current through them, and boil their water away. It is possible to desulfate an old battery, using a pulse type of battery charger made for that purpose. But it means taking it out of service to do so, as it requires very short but high voltage spikes to knock the sulfate crystals back into solution. The downstream electronics may not tolerate that very well. A standard DC current type of charger won't do anything to reverse deep sulfation. Most batteries would last longer if used with a pulser from day one.

 

Does your Prius have a conventional flooded cell battery in it ?? I was under the impression that all Prius came with leak proof 12V AGM batteries , as the battery is in the passenger compartment and could leak acid on the passengers in a wheels up accident if a flooded cell battery was used.

 

The Prius batteries are sealed with a valve, but they still vent pressure when they need to, such as when they start getting the above mentioned sulfation condition. It is possible to get into a sealed battery and check on the electrolyte condition with a little perseverance. It is possible to get some more life from a sealed battery by refilling the cells and desulfating.