12V Battery Replacement? Opinions Please

Your battery will probably be fine, but in case you need to replace it, I would suggest a Gel cell in order to prevent any possibility of acid leakage. My wife has killed the battery completely dead in our Miata at least five times and it keeps on ticking so far.
A load test will give you an idea of the condition of the battery, may not mean as much as you know because I don't think our cars put a high amp load on the battery
I'm considering one of these, works great in my TE450 Husqvarna, can't see why it wouldn't work as well in my Prius and lose a lot of weight http://www.ebattonline.com/

 

you are probably fine, just watch for weird unexplained events from your Prius in the next few weeks. A deep discharge doesn't necessarily kill your batt but with it being close to 4 years old it is in that threshold where it may not recover as easily.

 

Ummm, perhaps a car needs a huskier battery. If it does work out for you, let us know. My battery is nearly 5 years old with no DISCERNABLE issues yet so I'm not desperate for a replacement...

 

Considering that all the 12V battery has to do is boot up the computer and close the contactor to the traction battery, I really don't see why it would need to be any bigger. It's not like it actually turns a starter motor or anything. What are the specs on the OEM Prius battery anyway?

 

I've read that the 2010 Prius uses a special 12V battery and that normal car batteries are not to be used... see page 5 of the attached PDF file...

 

Good catch! From that document:

Why on earth it says that is beyond me. But it does say it :s

 

First an AGM battery is essentially a battery that won't leak, been used in aircraft for years. A gell cell is essentially a battery that won't leak also. Not leaking in a battery that is inside of the passenger compartment is probably what Toyota is after.
The E-Batt will provide enough starting amps to turn over a 500cc race bike for multiple starts. Pretty sure there isn't anything in a Prius that would pull nearly that many amps.
With the Prius it becomes a question of reserve capacity. Will the E-Batt povide enough reserve capacity to listen to the radio and run the fan etc. for 30 min or so? But I don't do that so I think it will provide enough for me. I haven't measured the current draw of the Prius yet, easy to do just haven't done it. But a lead acid battery makes as much sense as oil lamps for headlights. Traction battery isn't lead acid is it? Why is the 12V battery lead acid? Better question is why is there even a 12V battery to begin with?
My guess is due to safety concerns Toyota wanted the high power battery completely disconnected when the car wasn't occupied.
On edit, this link explains two types of SLAB "Sealed Lead Acid Battery" Gell and AGM [ame]http://en.wikipedia.org/wiki/VRLA_battery[/ame]

 

I suggest that you allow the car to remain READY for another few hours, if your daily commute does not require this amount of driving. If you make every effort to fully charge the battery, then you may find that the battery will survive this incident.

I don't think it is useful to pay for a load test as I've seen several posts from owners whose batteries successfully passed this test, then died a few days later.

After you've fully charged the battery, if the car continues to work well then there's no need to buy a replacement now.

The 2G battery is rated at around 35 Ah. It needs to be bigger than a motorcycle battery due to the following:

1) it is expected that a owner may want to play the stereo for a few hours while the car is ACC-ON, and it would be nice if the battery would deliver power for this purpose while retaining sufficient capacity to start the car later.

2) the battery capacity will deteriorate over time, so if you would like the battery to last 4 or more years then it would be a good idea to install more capacity than is needed on day 1.

3) if the DC to DC converter in the inverter fails then the 12V battery will be called upon to provide 50-60A or more (depending upon the electrical accessories in use at the time such as the cabin ventilation fan, rear defroster, PTC electric cabin heater etc.) so that you can safely bring the car to a stop. A tiny battery will not reliably provide this current for a reasonable length of time.

 

While the 12V battery doesn't power a starter motor, it DOES power the brake boost pump. When you press the brake pedal to get ready to press "ON" the car draws a 1/2 sec 50 Amp pulse from the battery. Then when you actually press "ON" it draws another 1/2 sec 50 Amp pulse. As soon as the car goes to "ready" it delivers whatever charge current the battery needs, up to 40-50 Amps. I saw 4-7 Amps when I did the testing on my one year old 2007.

Now, what do you suppose would happen if:
a) your battery was a tiny replacement such that the voltage dropped below 9V when the pump fires, or
b) your battery is damaged (sulfation) such that the voltage drops below 9V when the pump fires, or
c) your battery post connector is oxidized or the ground cable connection to the car chassis is oxidized such that the voltage drops below 9V when the pump fires?
I can't tell you but it will be curious and varied, as a computer(s) with a power supply that can't handle the load gives very interesting operational states!

DO NOT let a mechanic connect a standard "battery load tester" to your Prius 12 V battery! It's too small for those unless they can be set for very small batteries. It can be damaged by currents of 100 Amp and above.

Toyota wants the battery specified because it has a vent tube fitting, so if -something- should go wrong, the acid vapours and H2 plus O2 will be vented outside, not in the cabin. You can replace the battery with any AGM or gell type that also has a vent tube and that you can -safely- fasten down in the car. We're talking about a six cell lead-acid type only here. Anything else will require some engineering to match it to the charging system.

The GIII has a similar battery to the GII.

 

Yes, the 12V batt does power the brake boost pump when the car is not on ready. You can bypass the brake boost pump to start the Prius since the Prius Service Manual shows only the Brake Light Switch is necessary to "boot" the Prius and not the Brake Boost Pump. [I adjusted my brake light switch for quicker brake light. Now I just tap my brake and press the "on" button. The Brake Boost Pump is not activated. (As least not supposedly.) Should prolong life of 12V battery.]
The brake boost pump needs charge so you can use the brake in case the HV battery or Inverter is not on.
Brake Boost Pump is not that strong, but it's better than just using E-brake alone.

 

Thanks for the info in this. 12v in my 2005 died today so this is a welcome, upgrade replacement.

Was looking at the Braille battery, but doesn't seem like anybody used that in a Prius.

 

For better or worse, Toyota chose to put the 12 volt battery in the passenger compartment with you and your loved ones.

Under rare conditions, mostly involving overcharging, any lead acid battery can produce Hydrogen, a colorless odorless flammable gas. If it is a 'sealed' battery it can also produce a sulfuric acid mist if a seal blows. In the event of a wreck, sulfuric acid may be thrown around the cabin.

To reduce the risk of these events ever happening, Toyota equips the Prius with a externally vented Absorbed Glass Mat (AGM) Battery. The external venting solves both Hydrogen gas and sulfuric acid mist, while the AGM design reduces the liquid sulfuric acid to a minimum.

Very few externally vented AGM batteries exist in the aftermarket, but Optima makes one .

Optima BatteriesOptima Batteries DS46B24R YellowTop Prius Auxiliary Battery

Optima DS46B24R Optima battery direct fit replacement for Prius 2004 +