General rule on 12V battery life

While that is good advice for extended down time OR for those who make a lot of short trips.........

In general it might not be good advice because it will pretty much ensure that the car starts every day the first time regardless of the battery condition but THEN might not start the next time when it is "out in the wild".

Routine use of a battery tender when you don't really need to often will eventually bite you in the butt.

 

Meh, I like to hook up my CTEK 3300 every few months, say spring and fall.

 

Well, when do you "need" to?

I would say that if the battery is allowed to persist with open-circuit voltage below 12.6V, that it will start to sulphate. The purpose of periodically charging the battery is not to hide the battery's condition, but rather to maintain the condition at a high level. Then when you go into the wild the battery will continue to function.

Since a member is going to the trouble of monitoring the battery voltage, I would say one reason to gather that data is to do something with it - like charge the battery to keep it in good condition.

 

The best answer to that is:
When do you NOT need to.......when the battery is fully charged, or very close, every time you check it.

And sulphation is NOT a significant problem with AGM batteries.

A vehicle that is driven ~20 minutes or more in one or two continuous trips at least 3 times a week should not require any special attention to the battery.
If your trips are shorter or less frequent......or there is a long period of non-use, then there probably is some real need to periodically (or continuously) be sure the battery is topped up.

The "average" (if there is such a thing) driver should NOT have to connect a battery tender every night.
Just because some self-appointed "expert" on the Internet said it is a good idea doesn't necessarily mean that it IS; for sure not in ALL cases.

 

I personally have not advocated daily use of a battery tender. I think it is adequate to periodically use a battery charger. The next question is what period should be utilized? Obviously that depends upon individual driving usage patterns.

The Optima website recommends keeping stored batteries on an automatic multistage charger or if that is not possible, charging when the voltage drops below 12.4V:
Support - FAQs | OPTIMABATTERIES

If this benefits batteries left in storage, that practice will certainly benefit batteries that are installed in the Prius.

If a driver finds that the open-circuit voltage of his 12V battery remains above 12.4V after it has rested overnight, then he doesn't have to worry about charging it. I like to charge the battery at 12.6V but if you want to be lax about it, that is your business.

In exchange for keeping the 12V battery at a reasonable charge level, the owner should find that this habit is rewarded by a longer-than-normal 12V battery service life.

 

Good job of answering your own question.

 

Post #43 is pretty much exactly what I was going to say.

I daresay that Patrick answered his own question as a matter of necessity.

In this battle I'd say that Patrick has shown a better and certainly a more helpful dissemination of knowledge, which is what I come to the boards for.

Just to be clear, to whom are you referring as a self-appointed "expert"?

 

I don't think I've read anyone here give the advice to charge a full battery.

Just because it is not a significant problem does not mean it is not a problem. Any Pb/A battery, AGM or otherwise, will sulphate if left in a substantially discharged state.

From my recent investigation and monitoring, I have to disagree. It is better to monitor the battery voltage and charge accordingly. I choose to charge when my voltage is persistently at around 12.5V.

Absolutely, not probably. If the car is going to be sitting for more than 3 weeks for an extended period of time, then definitely continuously - with a suitable modern smart charger.

Again, I've not read anyone here giving the advice to charge their battery every night. If you are finding you need to do this, then you are certainly headed for a replacement battery as charging every night demonstrates the battery in question is in a dying state.

All in all, the advice to charge and how often, needs to be tempered against an owner's appetite for car maintenance and desire to see their battery last a good period of time or whether they are happy to just spend the money and replace the battery every 4-6 years.

 

Pretty much anybody who posts to a public forum.

 

Except you, of course. You're a real expert.

 

Bumping up an old thread. I have a 2014 PIP, brought brand new, currently with 108K miles. I still have the original 12v battery - peformed a load test at Autozone, and they say battery is still good. 9 years - not bad.
My Drive battery got regular Electric charge for first 7 years of it's Life, and only been charged sporadically since. Still get 17 miles on PIP. Does not burn any oil. Only thing I have done is changed oil every 10k or so, checked brake linings (and lubed the pins) at 60 k and 100k, topped up coolants and flushed the brake fluid. It has regularly had 2 or 3 long trips a year (500 miles plus), otherwise mostly commute.
Has been a very good ownership experience for me.
Just sharing my experience.