12 Battery Maintenance

491,000 miles - That must be a world record!

 

that is like 20,000 miles per mouth or 681 miles per day........ can that be?............or is it 49000 in the last 2 yrs.

 

I trust it was distiller water, found the same in my '06 Prius, that battery now runs the lawn mower

 

It would be except it says 41900.

 

Wait wait wait, these 12V batteries are supposed to be AGM, and not flooded cells. They are supposed to look dry. All the liquid is supposed to be hiding in the glass mat material between the plates. If I see free liquid, I'd be worried.

Furthermore, AGM batteries are sealed and only have a pressure release valve, for emergency conditions. It is supposed to release gas only when grossly over charged. So under normal operating condition it should lose no water.

Opening it and adding water does two things:

1) Diluting out the electrolyte out of spec;
2) Compromising the seals and create leaks later.

 

What is your reference? From my understanding, any battery mounted inside of the passenger cabin needs to be sealed, with the emergency pressure release valve venting to the outside. A non sealed flooded acid battery burping H2 into the passenger cabin is very dangerous.

Furthermore, all AGM batteries are sealed.
VRLA battery - Wikipedia, the free encyclopedia

 

I got a first hand look at my cute little battery as I needed to put my homebrew maintainer on for the winter months. It was a Sealed Lead Acid battery as I expected Kind of a tiny battery, no wonder they can get run down so easy Got me thinkin of a Li-ion battery...

Mike

 

Since the OP was able to easily open the caps and replace the missing water it was not sealed by definition.
Where is your reference it needs to be sealed or AGM?

 

Just the fact that every one of these has a vent tube attached, is indicative that they are sealed VRLA batteries. I do not have direct reference for them being the AGM sub-type other than it has been commonly discussed.
Sealed simply means H2 and O2 are sealed inside, from normal charging operations, and allowed to recombine into water inside slowly. Sealed units require a vent tube for oops situations of overcharging from a malfunctioning charger. Instead of exploding, it burps the extra gas through a pressure regulating valve into a tube, going outside.
Sealed does not imply that the unit is tamper-proof. I am sure you can open it. They need to be opened for recycling at the EOL.
VRLA batteries lose no gas or water, unless over charged beyond its engineering specification.

Here is a picture of a Classic Prius battery. Note the vent tube on the left, and the first warning written in English.


Iconic

 

The manual says that the stock 12v battery is maintenance-free. It is possible that the stock battery was replaced with one that does require maintenance.

- Spindifferent

 

Exactly, but it doesn't mean it's "sealed", AGM, or VRLA like some stated above.

If one wants to, we can place a wager. Just like here: Today: Tom and Ray settle a bet about "maintenance-free" batteries. | Car Talk

 

What they are talking about is a Maintenance-Free starting battery you find at AutoZone or WalMart. The Prius aux battery has more in common with the UPS deep cycle battery than a typical starting battery.

Sealed is a subset of Maintenance-Free, and AGM is a subset of Sealed. Some "Maintenance-Free" batteries are nothing more than a battery with some calcium in the plate formulation, and extra electrolyte to account for loss expected during its warranty period. These are mostly starting batteries. We seldom see under-hood starting batteries that are sealed or VRLA, because the nature of the service requires the battery to be charged at a higher rate, making it more tricky to seal in the normally generated gas. Sometimes, non sealed batteries are used inside of the passenger cabin too (mostly after market relocation). But these applications require the battery itself to be located inside of a sealed box, and the burped gas vented outside.

I wish Toyota would publish this outright and say it is a sealed AGM type, but they are not. I have not personally done an autopsy on one of them so I cannot say with 100% certainty. I do believe they are are sealed AGM type because:

1) Low charge current specified;
2) Built in vent tube that is characteristic of a VRLA;
3) It is widely cited as such online (take it for what is worth), and no evidence of the contrary;
4) The warning language on the label / general appearance;
5) The aftermarket replacement with the same vent tube placement, Optima, is not shy about it being an AGM type.

Other than these, I do not have any other evidence. I will assert that adding water, when explicitly warned against doing so by the battery label, does more harm than good.

 

Whether the battery is sealed or otherwise is NOT the relevant issue. What is relevant is that, having broken the seals the OP found that the cells were dry. If he had checked the voltage he would have found that it was probably down to around 11 volts rather than around 12 to 12.8V.
So why no electrolyte? Gel is a faint possibility but I don't think so. I believe that the OP did the right thing in topping up the cells with distilled or de-ionised water.
The Series 3 Prius charges the 12V battery at a voltage that WILL break down the water in the electrolyte by electrolysis into hydrogen and oxygen gases which are then vented by the tube mentioned earlier in this thread. Because the battery is sealed/maintenance free that lost water cannot be replaced other than by breaking the seal as with the OP.
I have started a thread here:-
Excessive Charging Voltage Kills 12V Battery On Prius 3? - Hybrid / Toyota Prius - Toyota Owners Club - Toyota Forum
describing my own experience and the very unsatisfactory response that I have received from Toyota's Customer Service Department in the UK.

If YOU have had similar failure of your 12V battery then please add to that thread.

And I would be interested to see if there is any constructive contribution from anybody at Toyota who monitors these forums!

 

Am I missing something here? Are you kidding that you need to add water to the 12-volt battery? I only saw people to do this 40 years ago. The model car battery should not need to do this. If so, I would like see the picture of your battery.