Another 12 Volt Battery Question

Was there a question in the original post?

Tom

 

I wouldn't worry about it too much. I've definitely left mine sitting for >2 weeks several times with no issues. I too don't drive much - I have about 2500 miles after 6 months - I commute by bike, and typically only drive on the weekends. And only then when it's somewhere (or for something) that I can't bike reasonably.

I did have the battery die on me once, but I believe that was due to the ScanGauge I had just installed failing to turn off. (Or perhaps an interior light, though doubtful.) That happened in about a week, but I have since left the car for much longer than that with no issues.

 

The Prius will take a longer to charge its battery than a non-HSD car because the 12V battery is supplied through a DC power supply that doesn't deliver as much current as an alternator. I would guess, and it's only a guess, that a Prius battery that is completely run down might take a couple of hours of running, or longer, to charge. On the other hand if the battery was not discharged to much 30 min a week might keep it up.

As Macman says don't worry about it, for two weeks it will almost certainly be just fine. If you do have a problem and it's to run down to start the car all you need to do is jump start it using the under hood connector and the directions in the owner's manual.

 

"How long can I leave my Prius and have it start?" This question is common and the answer is --- it depends.

1. How healthy is your 12v battery? If it is older (mine is 7 years old and is not as young as it used to be) and/or has been fully discharged a few times have a spare jumper battery in the trunk (I do and I make sure to keep it fully charged).
2. Is your 12v battery fully charged up when you leave? The Prius charging system is A "constant voltage, low current" system that protects the little 12v battery from over heating or out gassing due to heavy charging. This is a safe but slow charging method. Since the charging rate is less than 2 amps, it can take many hours of "Ready" mode to fully charge the battery. Short trips tend to lead to an undercharged battery.
3. What battery do you have? The OEM Prius 12v battery is a vented (in case of out gassing - unlikely, but possible in case of a problem in the inverter), Absorbed Glass Mat (AGM, relatively safe from acid spills) battery that might have a capacity of about 38 amp (some model Prii have a slightly smaller capacity battery) hours when new. You can get an Optima yellow-top battery (size 51) that is a little more robust when discharged (needs an adapter kit to fit right) or if you don't feel the need to vent the battery (not my choice, since I have never had battery problems in almost 181,000 miles of Prius driving) you can get another robust, higher capacity battery 55 amp hour battery (V Power Battery Model XPC-550). This V Power battery is comparable in capacity to a standard car battery.
   

JeffD

 

So far, I have yet to hear of a battery problem on any car that did not have an easy explanation - usually a light left on, door ajar, etc.

Ours sits for days and weeks at a time, with no problems. I still don't know where all this nervousness over the 12v battery comes from.....

 

The security systems installed by the port or the dealer may also have caused excessive battery drain. In my opinion it's a good option to avoid.

After looking at several of the other dead 12V battery threads I find there are quite a few people who have ended up with dead batteries after a few days or weeks. I believe there is a good possibility that several of them have done nothing whatever to cause the problem.

It is hard to discover what is going on because no one has done any kind of meaningful fault analysis on the cars that have had the problem, or even reported back that it has been fixed or not. Someone who has had the problem, my car apparently does not, needs to measure the battery drain with the car off and perform a test discharge on the battery to see if it can provide its rated capacity. Unfortunately the mechanics at the dealerships do not have the knowledge or the time to do this kind of analysis and those of us who would be willing to do it don't have access to a car that has proven to have a 12V problem.

I suspect it will remain unsolved until someone who has the ability and the time to do some testing gets access to a car, probably their own, that has developed a dead battery.

 

I came home after a 10 day vacation and found my Gen III would not start, just as described here and in other 12v battery threads. Luckily, I did not drive the Prius to the airport so I found it in my garage dead. I am posting here and will in another older thread to identify a couple of things that I discovered that were previously unknowns.

When you disconnect the 12v battery (to charge or replace), you do not lose the ECU dealer programmable settings such as seat belt and reverse beeper settings. My settings are just as they were prior to disconnecting. Driver and passenger seatbelt warning beeper disabled and reverse (backup) warning beeper set to one beep. Those settings did not change and my battery was disconnected for 3 days. The things that changed back to default or things that I lost were the radio station presets and the NAV system programming was lost as if it did not have the NAV data disc installed. All that was necessary was to allow the NAV to reboot and recognize the disc...however, it defaults back to the region it was factory set to, not necessarily your home region. The NAV does know where it is and displays the car on the map in the correct location, you just can't look up addresses as they system in my case reverts to the NE region instead of the south. So when you look for a city or street, it will be in that region. So you must set the NAV back to the region in which you live as well after a 12v disconnect.

The service manager at my dealer (Jim McNatt-Denton, Tx), tells me that they have had a number of 12v drain issues on the Prius that sat over 10 days. He tells me that most of them had no issues once the battery was charged again. He did say that they have found a number of batteries that had an internal issue and would not hold a full charge. This is the issue I believe I may have. After the vacation discharge, I charged my battery back up with a Pulsetech XC100-P Xtreme Charge. It will desulfate a battery and bring back a dead battery very easily. However, after charging and driving the car only 30 miles, after a four hour period, the battery was discharged and the car would not start again. I once again put the charger on it and when it was back to 100%, I tried to start the car with NO success. I was however able to jump the car from my truck battery and took it into the dealership today. Based on what I know and have observed, I believe I have a bad battery. These are AGM (absorbed glass mat) batteries and do not become as sulfated as a typical flooded battery, however, they can still be degraded due to sulfication to a degree. As for how a new battery develops a bad cell??? I don't know, but suspect that any degree of sulfation causes the current charge to build up going from one cell to another and stops against a plate that is sulfating between plates and either over or undercharges that plate...and it dies. My charger is capable or reversing this to a point. But it may just be a bad battery from the start. I run dual AGM's in my boat and would not give you a nickle for the optima batteries, I have another brand without near the return or trouble issues. But I have a great deal of experience with the AGM's and I also run a battery switch and ACR (automatic charger relay) setup in the boat. So I understand their characteristics and think my Prius has a bad battery, although I only tested volts and did not look at the amps.

I would also like to add that a battery under load will act differently than a battery that is static. You may show 12.6v and good amps on a static battery and put a demand on it and see a big drop. A good battery will hold up under load.

Sorry to run on and hope the info is helpful.

 

Install a battery brain from Batteriesareus.com and when voltages gets to 11v it will shut solenoid, and the drain - so the car will always start; after resetting the solenoid with a push of a button.

Using a deep cycle battery as suggested will maintain higher voltage under a drain, and longer, and require less of a re-charge from the vehicle battery.

 

Good information txav8r, unfortunately such items frequently get lost on this site. It is good that you rediscovered it.

http://priuschat.com/forums/gen-iii...v-battery-no-change-customizable-options.html

This site and in particular this forum needs a WIKI which would provide an indexed location for DIY information and facts such as this. Some other car sites have this and it works very well, but you need a moderator who has the time and knowledge to set it up and maintain it.

 

Thank you, I agree, some sites have an involved moderator to move good data and make it a sticky or start another forum for the data.

I wanted to update...it was a bad battery. Now, how did the battery get that way? No telling and as you said, the service tech does not have the time or inclination to keep the car the 3 to 5 days to allow all the ECU's time to attempt to power down and find the culprit. But some of that drain takes its toll on the battery over time so now mine was a dead soldier. The service manager told me it is a 325 cranking amp battery and it was putting out only 77 cranking amps at a full charge. That is the load I was referring to earlier. The battery will look good until they can load it up in test as if you were cranking and measure the output amps at that point.

I also want to clarify a few things about AGM batteries. Because of the glass mat that is between the plates, they are very stable and capable of taking much higher charges. They can also hold more of their available amps longer even though the ratings on them may indicate they are not much better than a standard flooded lead acid. An AGM battery IS a deep cycle battery and depleating it and recharging should not affect the life of the battery at all depending on how it is charged back and if it is never overheated. But unlike a flooded standard lead acid battery, you can leave an AGM in a discharged state without affecting the health of the battery once it is recharged again. My portable charger won't hurt it as a matter of fact, when it gets to the maintenance or float (other chargers use these terms), it is actually using two different current styles and that pulse actually will desulficate a battery (all batteries get this to some degree, some worse than others).

Having been a member here for a number of years, I have seen this as a good site in many ways...members helping members. But as PC has grown, I have not been active on any basis except when I needed info. I am glad to be able to contribute something because you guys have helped me a tremendous amount. Now, if they would just come out with a lockpick for the 2010 to do the things I want, then you guys could tell me how to install it! Thanks for all of your contributions!