2007 Prius - trickle charging 12v battery overnight

Our car often sits idle for a day or two, and what I've come around to is hooking up a smart charger, just leaving it connected. It's occurred to me that doing that might be a plus, for a service department, especially for protracted service, doubly so when the doors are often open.

It seems odd that negative cable disconnect is needed to load test. Again, again: research Solar BA5.

 

With all respect....

LOTS of fires caused by trickle chargers, even smart ones, because most have ZERO circuit protection built into the 12v side. I would NEVER leave a battery charging unattended (overnight, in an attached garage, etc), too much risk.

 

My CTEK's have inline fuses. And, I'm not going to sit watching it for 6~8 hours, lol.

 

What else you got going on ?

 

Rub it in...

 

Bosch S4 45Ah 12V 0092S40220 - it's about 60$ in Europe.

 

That's a measure of your charging system and doesn't give any info about the battery. Well, it kind of does. If it's reading 14.1V and your battery is low when the car isn't running, you know you've either run down the battery or it's not holding or accepting a charge. If it reads below 14V when the car is running, then there's a problem in the charging system. If your battery is 12.1V after sitting overnight, given its history, I'd change it before it strands you. You already spent the money. Easier to change it at home than in a dark parking lot.

 

I drove probably 400 miles between Plock malfunction errors on a 5 year old OEM 12v battery. Multiple starts including multiple short trips and multiple 100 mile trips between error messages. Didn't realize it meant the battery couldn't release the parking pawl. Cost me more in tow charges than a new battery did. Since replaced.

No idea why a more informative error message isn't available nor why Toyota service had no "just jump it and get the battery replaced" suggestion. All they wanted to do is call a tow truck to tow me to a dealer who was closed for the next 40 hours.

Since replacing the 12v no recurrences.

 

While it works, it is a flooded lead acid (FLA) battery. It typically has a lower operating voltage and is at more risk of running flat quicker when compared to the absorbent glass mat (AGM) battery that for which the Prius is spec'ed. I have a one of each in my Prii, so can offer some insight in comparing AGM to FLA.

This is not true. All you can infer from this is that the charging circuit has detected the 12 V battery is flat (or low in charge) and the charging circuit is in charging mode.

While that will solve your problem, 12.1 V after sitting overnight just means the 12 V battery is flat (discharged). While it will provide service well into the 11 V range, you need to get that 12 V battery on an external charger and ensure it operates most of its time at the 12.9 V end, more often than not, to ensure you get maximum life out of your Pb/A (lead/acid) battery.

 

You are driving around on a marginal 12V battery. It's going to give up the ghost at any moment without warning. Trickle charging it may breathe some life into it, but it's not going to cure it. If you relish the possibility of having to change the 12V battery with your new shiny (already paid for) one in the unpredictable circumstances, then by all means continue doing what you are doing. If it were me, I would install the new battery as soon as I received it.

 

Oh heck, once more: for a reliable DIY electronic tester: Solar BA5.

 

1) Load testing is most meaningful for cars that have a starter, that cranks the engine. The Prius 12V battery just power the various ECUs. The HV Battery cranks the engine.

To give you perspective, you can start a Prius w/ the small 12V SLA (Sealed Lead Acid) batteries found in home alarm components and UPS (Uninterruptibpe Power Supplies) for home computers. This type of battery will not be able to start a conventional car with a starter.

2) Read Post #5&8 to become a little bit more enlightened.
Is my inverter coolant pump slowly failing? | PriusChat

3) Trickle charge as needed, ideally w/ a smart AGM compatible 12V charger. If you driver regularly and never have a discharge event, like you did, you will never need to trickle charge. Some do like to trickle charge occassionally as "maintenance," as you recommend.

A discharge event leads to a shortened battery life. Your current battery will not live as long as it otherwise would have.

 

This *may* be just the clue you were seeking.....

Presuming the lube place did load test the battery, one of two things was likely the case:
- They used a standard load testing tool designed for high capacity STARTING batteries, which would just about ensure it failed
- The 12v battery is in fact weak and load testing it (even correctly) caused it to fail the test

In either case, it is very likely that the open circuit voltage was depressed to the point that it reset the clock and computers and would take the DC-DC converter a L O N G time to completely recharge it. Remember, the battery is only there to wake up the modules and the DC-DC is there to provide them with power and MAINTAIN the 12v, not to actually charge it - since it should never really be "discharged".

 

+1 to exstudent and 05PreeUs, these two posts have excellent information/advice.

It is not necessary to switch the headlights on and off 3 times. You maybe getting confused with how to access the vehicle check screen, in which one of the methods it to switch the PARK LIGHTS on/off 3 times while holding a button on the MFD. Just switch the headlight on and leave them on.

More importantly than the actual voltage, is what the voltage is at when the voltage stabilises (relative to the starting voltage) and for how long can the battery sustain that voltage under the load of your headlights being on. Anything under 10.5 V for anything less than 2-3 minutes is going to give you problems with the electronics.

You will need more like 24 to 36 hours of trickle charging to charge a flat 12 V battery. Further, the frequency should be more frequent than once a year, but entirely depends upon how long at a time your car sits unused. If it was sitting for more that a week or two without being used, then on with the trickle charger. Furthermore, the charger (and I'd recommend a proper 4 Amp charger in this case) should immediately be used anytime the battery is significantly or fully discharged.

Hope that helps.

 

…whenever I leave the car in the garage I plug it into in the maintenance charger (via a quick-disconnect) so the 12V AuxBattery gets topped up. The car has sat in garage since last Saturday night, and with the colder weather coming, I'm sure it will spend even more days in the dry and warmth of the garage.

 

Another trick, especially if the car is out in the elements, electricity out-of-reach, and/or going to be out of commission for some time, is to fully charge and then disconnect the negative lead. It's the dang background drains that slowly pull it down.