12v Battery Query

agree^^^ where did you get the new battery?

 

11.5 sounds really really low.

My 4 year old battery is at 12.5 with a load (lights on, heater full blast, etc) of 11.1.


Edit: just saw your 12.9 test post.


iPhone ?

 

The 12V is not a "starting battery". It's a "power the electronics battery, so the HV battery/inverter can do everything" battery. There is no "starter" in the Prius. The 12V never "cranks" anything.

It's a low capacity, low CCA deep cycle AGM. 11.5V under accessory load isn't an issue - provided you confirm the resting OCV is > 12.6V.

An actual load test would definitively say your battery is good/bad, but I wouldn't expect any issues with the numbers you've reported.

 

How does the charging system work on a 2008 Prius? We own a Prius, but also have a 2007 Camry hybrid and assume they work similar to keep the 12v battery charged. No? The Camry hybrid battery was replaced, only to discover the car would not run at all after the replacement. The mechanic charged the Panasonic battery and I drove 20 miles home, only to have it die at 19 miles. I was able to get it home and put a load (headlights) on the battery. It dropped to <10v rapidly.

So I replaced the 12v battery with a D34 Optima Yellow Top and the car started fine. However the voltage at the battery was only 11.6 and slowly dropped to 11.35 so I turned off the car and disconnected the battery.

Shouldn't there be at least 13v+ at the battery when the engine is running? Could there be a connector at the hybrid battery that was not connected when replaced? There are no warning lights on the dash and no codes on the Actron reader.

 

On the Prius, it's the hybrid inverter under the hood that charges the 12V battery. Typical charging voltage is 14+.

If your Camry died on the way home from a hybrid battery replacement, there's likely something very wrong with the hybrid system, and a 12V battery voltage problem may certainly be a symptom. Assuming you got some warning lights, you need to get those codes read.

 

The charging system had to be working prior to removing the old hybrid battery as it was driven only on ICE for probably 75+ miles.

I'm wondering if the mechanic that installed the hybrid battery didn't reconnect the low power connector on the hybrid pack.

 

What's that?

 

I'm really coming around to that. If you're driving a car at most once a week you're likely going to have troubles: Modern cars have low level but persistent voltage draw. Would it be modern electronics, or?

 

Go to 6 min in this video.

 

Thanks.

And you think this could happen without a check engine light?

 

The check engine light will come on when there isn't enough voltage to operate the ECU et al, The entire dash will light up including the 'Check Hybrid System' and 'Check VSC(?)'. Until then, the car will drive as normal; no check engine light, no red battery light, nothing. It will just die. Put in a fresh battery (in this case a brand new one) and it will start and drive normally. However, the battery voltage will slowly drop to below 12v. Turn on more accessories and it drops further......still with no warning lights.

Check the voltage at the battery and accessory plug in the passenger compartment; it will be the same and continue to drop until the car simply dies. The voltage at the battery, if the alternator (or whatever it's called for a hybrid) charging system is working correctly should easily be over 13v.

 

Yes, you are correct DC/DC Converter (which is what it is called) should be supplying a charging voltage of anything between 13.5 V and 14.7 V if it is working correctly, usually somewhere around 13.8 V if the battery is healthy.

To me, it sounds like the DC/DC converter (part of the inverter) is not working.

PS, charge up your 12 V battery with an external automatic charger to avoid permanent damage to it.