12V battery - 2008 Prius - replaced but not bad - interesting to me

My 07 driven 45 miles 5 days a week keeps the 2 year old Optima Yellow top charged to 12.7 volts as measured in the am with my Fluke
with car off. Just did it the other day. Which is exactly what I expected.

So at 11.9 your not even close to keeping it charged properly.

 

o/p, what are your driving habits like? perhaps not enough to keep a full charge? i agree a monthly charge is a good idea.

 

Isn't the 12v is not charged directly from the alternator but rather via the traction battery. The 12v powers only all the electronic gadgets like the radio and security things like doorlocks and smart key response. So one would suppose that your traction battery or the circuitry which knows when the 12v needs a charge and does it is somehow marginal. Or you have some sort of drain which is causing the voltage drop. Any special aftermarket installs? Any reason to suspect any lights staying on? How far away from the car is the key kept at night or when the car isn't in use?

 

Scott I would check the voltage with another meter. 13.5 volts after standing overnight would be a very high voltage for an AGM battery that would more typically be at around 12.8 to 13.2 volts for a new battery fully charged. 11.9 volts is a low voltage and state of charge off load.

John (Britprius)

 

Prius charges the the 12 volt battery just fine it just needs a minimum time to do it. Given the small size of the battery and the constant keep alive draw its subjected too and the many ridiculous things people do to it I think it does quite well. My stock battery lasted 6 years.

And yes not many batteries would keep a maximum charge for weeks even just sitting there. Much less even getting a battery to charge to 13.5 volts and keep it.

 

Good plan. A similar result can be had with a nice long drive every couple of weeks or so.

There are many other threads from owners in similar situations who have come to the same conclusion.......or have decided not to worry about it and change the battery every couple of years.

What "other information" would you like to have ?
There are several hundred threads on here about 12 V batteries and the charging system already.

The situation is not unique to the Prius. It applies to all hybrids with small batteries that are used infrequently.
An AGM type battery helps but doesn't completely solve the problem.

 

Your figure of 1 amp is off to the power of 100. Typical current draw for a Prius with SKS is 0.015 amps, less if the car does not have SKS. With a draw of 1 amp a fully charged battery would be considered deeply discharged " above 50%" in 24 hours. In 48 hours it would be unusable.
A good AGM battery "Prius" should be higher than 12.5 volts more in the region of 12.8 to 13 volts. A voltage of 12.5 would suggest a charge level of about 75%. Not a level of charge to leave a battery sitting at for months.
A good ordinary flooded battery should read 12.6 to 12.8 volts for a full charge, but the self discharge rate is much higher than AGM batteries so a monthly recharge or a maintenance charge would be recommended.

John (Britprius)

 

10.5 is not normal, but I find it hard to believe the system isn't able to keep it charged. The 12V DC system is capable of providing 100 amps, but because the battery is small, it's attenuated below that to protect it from over-charging. My first guess would be a loose connection, or something wrong with the charging circuit. It's not clear from your post whether you measured the charge-level after leaving it parked for awhile, or if this is a running-average of the typical charge-level. If you have after-market accessories, they could be draining down your battery more than you realize. I've heard of GPS tracking devices that will drain a good battery in two days. Are you sure that the FBI isn't watching you? Sorry, just a joke.

 

It seems that you find a lot of things regarding electricity "hard to believe".
You don't really have to keep reminding us.

Except in extreme or extraordinary circumstances, "the system" IS able to keep it charged.

 

Got a bee in yer britches again? Wish I could help.

 

Vitamin B12 might help.

 

And I am quite sure that it does NOT.......at least not the way you have described it.

IF.....the battery is healthy and the applied charging voltage is over 14 volts, the battery WILL charge significantly.
Then it is just a matter of how LONG the charging voltage is applied and how much time the battery is drained when the charging is not taking place.

Your 10.5 reading indicates that the battery has developed a high internal resistance, causing the voltage to drop with just a little bit of current draw; it is worn out.
OR.....you are measuring it when the car is not really OFF.

I don't think we have the whole picture yet.
What do you intend to do to help your new battery last longer ??

 

Just take the battery out while it's running and report your observations back to us.