Recharging after Dead 12v Battery

+1 on trying a second mechanical key if you have it. Sometimes one may not have been cut properly. Good luck and let us know how it works out!

 

A timely reminder of why it is a good idea to periodically use the key in the lock.

 

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Thanks - I'll try this tomorrow!

 

OK! thanks for the info, I'll try this in the morning!

 

Thanks, I'll try my second key tomorrow! Will post what happens.

 

Yes, CO is Colorado - thanks for your help; will let you know how it turns out.

 

Was able to get the Prius car door unclocked with the emergency key today! Now I can slow charge the battery. It is very cold in CO now and wonder if I need to wait until it warms up a bit to recharge or if the cold won't affect the charge?

 

how cold? how old is the battery, maybe you should just replace it.

 

Hi Bisco, it's 19 degrees outside right now; the battery is relatively new; a year or two at the most. I'll have to look up the exact date.

 

i think you can trickle charge it, is it a smart charger? they usually will not charge if too cold.i think lithium is more sensitive than lead acid.

 

I was able to get the Prius car door unclocked with the emergency key today! Now I can slow charge the battery. It is very cold (19 degrees) in CO now and wonder if I need to wait until it warms up a bit to recharge or if the cold won't affect the charge? The battery is only a year or two old, at the most. I need to look up the exact date of purchase.

 

Glad you got into the car! Maybe pull the battery and charge indoors where it is warmer?

 

That's great girl. Slow charge away the battery will warm up nicely. Go 2 amp mode for an hour then go 10 amp mode till the full indicator on the charger comes on. Smart play you will not hurt the car just needs patience.

Then hopefully it will hold enough charge to start the car. Start making plans to replace that battery as the way it was perfectly discharged it will never be reliable again. To cold out there to be stranded.

Good luck!

 

Don’t charge the aux battery more than 3.5a rate — it says that in the manual, on the battery, and it’s basic lead acid sense.

 

Look also for a label on the actual battery. Mine has a sticker advising 4.2A max. I'd go by that rather than the manual.

 

I have read that's the best option for using an external charger for AGM batteries - going at 0.1C- when you can do that.

Just FYI that never happens when you actually start (ready) the car. The dc-dc converter is a constant voltage system so it will supply around 13.8V at up to 100A. The AGM will accept as much current as it can take. So if your Prius sits for a couple weeks and you get in and it has enough to Ready up, then you could be hitting the AGM with 20 or 30+ amps until it levels off.

Posted via the PriusChat mobile app.

 

Are you sure about that, because my observations IRL does not support that?

I, for sure, see variable voltage and suspect that the current going into the 12V battery to be variable too. The amount of time it takes to get the charge into the battery does not support the high currents of the order you indicate.

Can you direct me to the source on which you base your conclusions as I'd be interested to read up and expand my knowledge?

 

I agree dolj it does not work that way, it did about 50 years ago though...

 

The Prius generation matters too. This is the Gen 2 forum, and the Gen 2 DC/DC converter puts out about 13.8 volts.

At that voltage, the maximum current I've ever seen into a dead, clobbered, just-jumped battery was about 8 amps at first, and quickly tapered off to below the 4.2 amps suggested on the battery label. And that's why you need a good 15 or so hours in READY to recharge a flat Gen 2 battery.

If you ever move to a Gen 3, where the converter puts out 14.7 volts a lot of the time, that nearly-a-volt extra makes a huge difference to current going into the battery, and you see the numbers AHetaFan measured for Gen 3 charging current, up to 70 amps at first rush. But Gen 3 also has a temperature sensor on the bracket above the aux battery, and the ability to reduce the converter output voltage when it thinks it should.