Battery Maintenance - Revive your Dead or Dying 12v Aux Battery

While on summer vacation last year I encountered 12v battery problems on my 2010 Prius. Reading some issues recently reminded me of those situations and motivated me to share my experience with the community.

At the time I was new to the car and was surprised to find the car will operate without too much fuss with a low to almost dead battery... (based on my knowledge of traditional car battery requirements).

In a conventional (non hybrid) car, the 12v battery will let you know its got a problem real quick when you go to start the car. A low to dead battery translates to sights and sounds that are real noticeable. (rar... rar... click... click, etc). A traditional car requires high current capacity to start the car while the Prius has much lower requirements. In the Prius, all the 12v battery has to do is provide enough power to perform the computer start up tests and click in the HV relay so you can get the "Ready" light lit. Once you get the Ready light you are golden as the 200+v battery kicks in and provides power to the 12v bus..

When I started having problems I was still new to the car and though I was doing something wrong. I would turn it off/on and press the power button differently and all of a sudden it was fine. But... soon it began to happen more frequently... and all of a sudden it was very fussy to start in the morning. Time to investigate...
Once I got my hands on a voltmeter I was shocked to find my battery was below 11v.

Daaa... no wonder the car was so fussy to get the Ready light.

From a car "start" perspective.... The 12v battery's main goal is to power on the HV Relay so the big HV battery can take over and do the heavy lifting (such as crank starting the gas engine). Once the car is in the "Ready" mode the HV battery is involved and the 12v lines will rise to about 14.5v. At this point the little 12v Aux battery is no longer a major factor.

In my case I didn't have any issues until the battery was hovering below 11v. Once that caught my attention I was quit surprised at the condition of the battery and how insignificant the 12v requirements are to the overall system. Lead acid car batteries are 2.1v per cell so a 11v minimum load reading indicates a serious problem.

In my case I was able to do some minor maintenance to the battery and quickly bring it back to life. With minimum effort you can remove the battery from the trunk and perform some maintenance. When mine stated to go south I was amazed that the battery was very low on water. Simply adding distilled water brought it back to life and as a result its been fine for the past 8 months.

Since then I've seen the same issue on another Prius... but this time I caught it before the the water levels got too low.

Attached is a picture of the standard battery with the fill holes exposed.

As I recall the steps are as follows:

A. Using a 10mm wrench, remove the battery from the car.
* Loosen and remove the negative and positive battery posts from the battery.
* Remove the top metal battery bracket.
* Unplug the battery vent tube.
* Lift the battery out of the trunk with the attached battery carrier.

B. Remove the top stickers to expose the clear battery cover.
This clear cover is glued in... I used a razor blade and cut it out along the edges.
Later I just poped it back in and put the stickers back on... but you can also use superglue or other selant on the clear battery cover.

C. Remove the 6 rubber caps that cover each cell.

Next shine a light in each hold to check the water level. In my case the water was too lower and plates were exposed.. I added water, charged the battery and all was well.

If you've been fortunate and had the same batter for the past x years you may find that this simple
"water check" maintenance will extend the life of the battery and keep you going even longer.


*** Final Battery Status - The battery lasted an extra 2 years. See post #41 for details.

 

Thanks for the feedback... this post generated more thought provoking ideas than I expected. I'm happy to note the battery is approaching an extended 9 months and is still going strong with a nominal 12.2 volt measurement (as measured in the morning with normal load). Of course the voltage immediately rises to ~14.5 when in the ready mode.

I'm amazed at a few of the crazy responses I received on this post... I didn't see this issue as such a big deal... the water was low so and I added water and the problem was solved.

I would generally do the same thing if it were the engine and it was low on coolant. (I would also screw back on the top after refilling). However if it continued to leak I would seek out the root cause.

Over the last 9 months... if I had issues I would have looked further but it hasn't been a problem. The battery has been operating fine and there is no spewing of acid in the battery compartment.

Lets break down some of the other feedback into manageable chunks:

Assumption A: "Your battery won't last long"

I already mentioned that the battery has lasted an additional 9 months.

I think the proof is already in the pudding from the initial post.

The cells were low on electrolyte/water and the battery was not able to reliably start the car.

I don't think there's any dispute that adding water to the battery is a bad idea. Surely most everyone would agree that having the fluid at the proper level is better on the battery and will allow a longer life.

Before I opened it up it was dying/dead and had no hope. By one person's definition, my only option would be to buy a ~$200 replacement. By intervention the battery has proper fluid levels it is operating fine and has extended the life for 9 months and counting.

Not sure about everyone but if I find a dead/dying SLA battery I would approach it like any other problem... troubleshoot and propose a solution.

Assumption B: "the next time your remove it you might be amazed to see all the corrosion that has happened in the battery pan."

Can you show me where you got this idea from?
Do you know of many others who've had this problem with the Prius?

I've check the battery and the compartment... There is no doom and gloom in the cargo area. The battery is operating at the normal ~12.5v range with normal load and 14.5 while being charged by the HV battery. Adding water did not turn it into a voodoo battery with magical capabilities. The battery has the same rubber caps covering the same 6 holes as it had prior to the maintenance. The clear window is in place with the same stickers and the same vent tube is still open to the outside. I also mentioned about the sealant and the stickers over the clear cover.

Assumption C: "Most sealed batteries on the market today are AGM type, which function similar to GEL cells, and they do NOT lose water over time."

Since you know more about these batteries that most...

* Can you site your source for this claim and over what time frame will they "NOT lose water"?
* Is the primary seal from the rubber caps or from the clear cover?

<< If I manufactured batteries, I would hope you would never refill the battery if it ever gets too low (as this would increases my sales). I also believe similar things can be said for almost any maintenance situation. You could never extend the life of your home's water heater by draining the tank or changing the anode. And of course one should always replace their mattress at least at the shameful 8 year mark. >>

My opinion is... under various scenarios they do loose water and my claim is that's a bad thing. Simply replenishing the water is a good thing... I don't claim to be a battery expert but I believe they have a vent hole for a reason. I also believe once the fluid has escaped its not magically going to find its way back into the battery... And once the level gets below the plates the battery is going to have a shorter life span.

So today I don't have an answer to why the battery fluid was low... perhaps one of the rubber caps was not sealing correctly. Perhaps leaving the lights or radio on for extended times over stressed the battery or perhaps it's just lasted longer than the expected time frame for it to "NOT lose water over time".

If they do lose water over time for one reason or another... is someone really against topping up the battery and re-sealing?

If there's something important to learn here... I'm all ears... If adding water to a battery is "VERY bad advice" what is your recommended solution?

 

Once you remove the rubber caps you can see the plates and levels... it's just like looking into any other battery.

More akin to a motorcycle battery except instead of 6 screw tops to unscrew there are 6 rubber caps to lift off.

 

Wow... your batting 100%... most every statement you've made in this thread is off base.

Where are you getting this information from?
Do you always just making it up as you go?
Is this your opinion or just for entertainment purposes?​

I'm trying to be polite and don't think its appropriate to continue to waste others time and energy reading all this extra nonsense... but frankly I don't like the way your making all the crazy conflicting statements without backing them up with facts or where you get the ideas from... However I do have to take exception to you latest statements "something wrong........with the battery or the charging system or with how it is used."

If your understood electronics or charging circuits you wouldn't makes such desperate statements. You clearly don't understand this area. Your other comments "get your car to a mechanic" and "high charge is a response to your battery" only confirm you are way out of your area of expertise and are clearly making this up as you go.

a). You made a big fuss about the 14.5v measurement. Show me where 14.5v is too high for the situation I sited?
You won't because like our other comments...You're wrong again...

My opinion is this is normal and if you think differently... please tell us where your getting this info from or simply tell us what you measure. When or if you do... I bet the measurements are in the same ball park.​

Doing a quick search on this site shows many threads where the data loggers and real time scan gauges confirm that 14.5v is normal.

Here is the first one that I found but there are many... because in spite of what you claim (but can't back up)... this is how the car operates.
http://priuschat.com/threads/should-it-be-13-7-or-14-7-volts.103036/​

These are the facts (not the crazy doom and gloom statements you keep stating... but can't identify a single reference to confirm your position).


b). Where did I say mine is 14.5 "continuous charging"?
I didn't... you made that up. Please read my post.

I stated the battery level rose from 12.2 to 14.5 in the morning when I changed to ready mode.

I never said it was constantly at that level. Also contrary to your bogus statements, 14.5v is not extreme but in the normal range of operation.

This is all about the car's design... nothing about the battery.​

c.) Your statements "Since they are truly, completely sealed you would damage the case trying to open it."

Are you kidding me... "completely sealed" and "damage the case trying to open it."​

Welcome to the real world... There is no such thing as "truly, completely sealed" battery.

If it were so, the battery would not need a vent pipe.
​

You made an earlier claim about "A real AGM battery either has NO vent at all or one that is controlled by a "pop-off" valve of sorts."
What battery are you talking about?

We're not talking about a theoretical or fantasy battery you have in your head.
We're talking about the standard 12v battery that comes in the Prius (as I recall the Yuasa S46B24).

If you know something about this battery, please share something that's based on facts.​

Did you even read my post or look at the picture of the battery?

I bet you have not even looked at the mechanics of these batteries?
Adding water to this battery is a piece of cake.
If you knew anything about the battery you would have to acknowledge some facts.​

d.) Your comment "Didn't he say that he had to dig out glue/sealant to get the cells open ??"
No I didn't say that... you misrepresented the facts on that too.

The conversation was about viewing the cells though the small holes once the top is removed.

Removing the 6 rubber caps and viewing the level is in fact analogous to removing 6 screws and viewing the fluid levels in a typical motorcycle battery.​

e.) Your comment "Things that come sealed are meant to STAY SEALED."

I know "Sealed" batteries are not suppose to leak or lose water under manufacture's recommended situations... but this is the real world and batteries get stressed in various situations. The Titanic was never suppose to sink either...

If you want to hide your head in the sand and ignore the fact that the battery does lose water and can easily and safely be repaired by adding water and resealing... that's your opinion. Please just note that this is your opinion and stop telling everyone you disagree with you that they have "BAD advice" (especially when you cannot site a single reference for your claims), Making claims that you can't back up is confusing and is a waste of everyone else's time.

Your solution is ignore the fact that the fluid is low and toss the battery and spend $$$ to replace it... mine is to troubleshoot and solve problems. I didn't post a theory with "made up" conclusions. I posted a real world example from two different Gen3 cars. Both had low fluid levels and both were enhanced by simply adding water.

This is a common sense solution to real world problem. This is not the rocket science you are trying to make it into... my battery was dead, I troubleshot the problem. I confirmed it was not the car (if we had time to sit and have a beer, I'm confident I could teach you many things is this area but right now just trust me... the battery was the problem).

I know "you" believe a "sealed" battery means it's never to be opened and can't be done without breaking and destroying it... but the facts are... this battery (The standard Prius battery)... is easy to access and easy top off with distilled water. I did so and the results are now 9 months down the road. The battery has started the car just like a new one from July through May without exception.​

Enclosed is a picture of the battery... Its not broken or damaged. It looks just as it did before the maintenance.
The only difference... its no longer dead... its was revived by added water and still going strong.

Please excuse my frustration... It should not be this hard to share ideas and solutions. If I'd known this subject was going to generate this much non sense I would have never bothered posting. I would ask you to be realistic... this is the real world... beep happens.

This is a great forum where sane people help each other and share ways to fix problems and extend the productivity of their beloved cars etc. I look forward to hearing and sharing positive posts from you in the future.