12V Battery

Well, it's time! After 3 years the GII I had required 12V battery servicing (shown by low voltage after sitting overnight). I was able to add distilled water to that battery, after peeling the label off.

So today I connected a temporary 12V battery to the boost point in the GIII (Pearl S) and removed the 12V battery in the rear, as it's showing rather low voltage after sitting overnight. Down around the 10V range! Panic time. Winter is coming.

Took it inside and pealed the label off. Yup, the manufacturer doesn't want me to add water. They -glued- a plastic cover over the fill caps. Well, being well trained by my economical friend, I broke the darn plastic off to get at the caps. Several cells had the electrolyte down below the plates. It always seems to be the end cells first. Not sure why, in a "sealed" battery.

Before doing anything I had connected my high tech battery tester and it indicated it was at "20%".
I added distilled water until all cells had liquid well above the plates. There is no indication of how much to fill (because you are supposed to just buy another one) so I was kind of flying by the seat of my pants.
Put the battery on constant voltage charge at 13.8 V and it started at about 15 A, but after 10 min. or so it was down to 2.5 A. I let it charge for about 30 min. to "stir" the electrolyte and put it back on the tester. It read "70%".

Left it on charge, and will test it in a few hours and put it back in the car. I'm also watching for leakage current once it's fully charged. That indicates cells are shorted by sulphate buildup and chunks of lead that can fall off the plates once they age too much.

With the GII I could say it's a good idea to do the "add water" exercise (that GII battery lasted -7 years-).
With the GIII battery I think it best to just replace, unless you are -very- comfortable messing with lead acid batteries.

I'm impressed with how much easier it is to replace the battery in the GIII. In the GII you have to move the Traction Battery vent tube. The GIII battery just lifts out after the clamps are removed.

After a few hours the charge current was down to 1A. I didn't want to leave the car with the temporary battery connected too long, so I reinstalled it. On test it still indicates "70%". This is a "Pulse battery Tester", and so far, seems to give pretty accurate results. At least when it says the battery is ok it doesn't seem to fail at the "worst time" (which is when they always do).

 

AGM batteries are "absorbed glass mat". That is, the electrolyte is "held" in a glass mat. It's still the same electrolyte. Adding water works just fine, as proven with Pearl, when I added water in 2010. That battery finally failed early this year, after 7 years of use. As I mentioned above. The funny part is there was liquid electrolyte -above- the plates/glass mats when I pulled off the caps on the 2012 battery, on three cells. This battery uses rubbery caps that sit over a tube that sticks up from the top of the top cover (in the channel made for them, and covered by the glued on clear plastic). They allow pressure to escape, but they don't allow air back in (they all held a slight vacuum when I removed them, releasing the vacuum with a soft "whoosh"). That channel is vented by the vent tube all Prius 12V batteries have. Well, it sounds like the G4 may not have it, as I hear that 12V battery is under the hood.

This morning, my voltage was at 11.8V before I put it in "ready". Nice change from down around 10V.

And no, I won't be "stranded", as I'm looking after my lead acid 12V battery.

Check your battery voltage first thing in the morning, Tideland, before you put it in "ready". If it's below 11V it's probably getting close to "time".

You could check to see which construction it uses. Just peel back the label to see. Pearl's battery had a long plastic cap over the channel that just pulled off (not glued). Under that was the channel with individual "caps" that could be pulled off with pliers, and distilled water added. I use a piece of tubing, which I immerse in the distilled water, hold my finger over the top end, and remove, allowing me to place the bottom end over the cell and remove the finger, dropping a small amount of water into the cell. Better control of how much is added, and much easier to avoid covering the entire hole with water so it won't enter.

 

There have been many "assumptions" in the replys.

I use a "pulse battery tester". I referred to it as "my high tech battery tester". In my many years of testing batteries I have found you have to match the tester to the application.

A "starter battery" is best tested with a load tester. The Prius 12V battery IS NOT a "starter battery". CCA has NO meaning to a Prius. A high value indicates the manufacturer put in heavy intercell connections. Or lied. As the Prius only draws about 50A from the 12V battery, and only does so for a second or so, a high CCA value is not needed.

A battery intended for electronics power supply "off the grid" needs to be a deep-cycle type. These generally don't do well if used for cranking an engine, but do very well at lower current loads, such as the Prius. The Prius CAN use a starter battery, but doesn't need the CCA ability. A high CCA value -may- make the battery "better", but most likely will have no meaning in a Prius application.
A deep-cycle or non-starter battery is best tested with a pulse battery tester. I include gell cell batteries in this group. My pulse tester was sold to me by a company that specializes in alarm systems and such. It was selected by them to offer to this group of customers because it is the best testing device currently available for the batteries they use.
BTW, while the Prius 12V battery was removed from the car I used a gel cell 10A-hr 12V battery sold as an alarm system battery, to keep my settings intact.

While "servicing" my Prius lead acid battery, I used a digital voltmeter, directly connected to the battery. Its' accuracy has been confirmed in various ways.
Once in the car, all voltage readings are from the Scanguage II. Remember, it reads the voltage on the OBD port, which is at least 20 ft from the 12V battery. Without doing a research project, I have to "assume" (we all know what that means, right?) the reading from it is accurate. But I'm only using the readings as a comparison, so it really doesn't matter. Before service, the 12V battery read around 10V after sitting overnight, and before the car was turned "on". After servicing, it reads 11.8V. To me, this indicates the battery is "better", and probably "ok" for a few more years.

Finally, the charge current. The battery label does indeed indicate you are to use no more than 4A charge current. The -reason- for that is they don't want you to cause a large amount of gassing to come out of the battery. For whatever reason (you can't replace the water lost, you might dislodge the caps, etc). Starting the charge at 10 to 15A, which then very quickly tapers down to 3A IS NOT going to harm anything. In fact, it may clear off the plates (dislodge sulphate buildup), but must, of course be done -carefully-. I assure you, I WAS -very- careful. In the car, I would bet money that this same higher current happens. I have noticed, ever since I first got Pearl S, that after sitting overnight, the 12V system voltage runs around 14-14.5V for the first 20-30 min., then drops to around 13.5-13.8V. After servicing the battery I see this same behavior. I'm guessing this is the "smarts" built into the inverter battery charger. Charge the battery back up, then go to "float" voltage.

An interesting note, that while charging, the power supply I used was one I built that has both voltage and current limits settable from the front panel. I attempted to vary the charge current, trying to take it higher than the 2.5 A it was running after about 10 min, by increasing the output voltage. The current stayed pretty constant (the limit was set to about 15 A), even when I turned the output voltage up to 15.5V. I've seen this before while charging batteries of various types, but thought it WAS interesting.

 

It appears to be a low cost pulse tester (they call it a "conductance tester"). Can't comment on how good it is. If it works, I'd say it's good. By "works" I mean if it says a battery is good, and over the next few years that battery IS ok, then it works.