Some measurements on 12V battery

OK OK, I'm guilty. When I bought Pearl I also bought a Battery Tender. That was four years ago. Yesterday I finally connected the "pig-tail" lead to the boost terminal. My excuse is I'm a tech and I don't fix things that aren't broke.

I'm still using the original battery, and due to using Bruiser a lot last winter I was getting indications the battery may be running at low charge (Scangauge showed higher than 13.8V running voltage). Lets just say I was suspicious of the health of the battery.

So I connect the Battery Tender and plug it in, along with a meter to see just what voltage it will charge to, and what the voltage drop is between the boost terminal and the battery (pretty much zero at 1.25 Amps that the Battery Tender puts out). The battery voltage slowly moved up for about 20 minutes then jumped from 13.8 to 14.2. The Battery Tender didn't switch to the "fully charged battery" state. Hmm. This indicates to me the battery is "fully charged", and that I'm not happy, as 14.2V is too high for a "float battery", which the Prius one is. So I'm STILL suspicious of the battery.

Also, with the Battery Tender on the battery, when I opened the hatch to connect the meter the voltage stopped rising and started slowly falling. The car draws more than 1.25A with the hatch open? All interior lights are off, except the door lights, which can't be turned off. So I put the meter in the hatch area and closed the hatch, then stood by the fuel filler door (to make sure the FOB wasn't seen) and the charging resumed as before. Funny.

Looks like I have still more work to do. I DO have a fancy "pulse load tester" for larger lead acid batteries (ZTS, Inc. - Pulse Load Multi-Battery Testers™) and it indicates the battery is down to 40%.

Fun with the 12V battery!

 

I was reminded by a friend that two incandescent lamps (the two door lamps) DO draw about the same current the Battery Tender puts out. So it would affect the circuit. I may re-do the experiment in the next few days, staying in the engine compartment and leaving the doors closed.
I don't like going out there (to the garage) at this time, as I get surrounded by a cloud of mosquitoes. It's been a wet summer and they are very healthy!

 

Re-did the test today. Battery started out at 12.5V after sitting for 20 min or so after driving it. Took about an hour for the Battery Tender to go green flashing (maintenance mode). Voltage was at 14.28. Call me old fashioned but I think this is too high for a float voltage, especially at 22C. It would cause the battery to loose water.

I may add a diode in series to drop it a bit.

 

OK, I finally got "off my butt" and started work on Pearl's 12V battery.

First, thanks to Bernard at eLearnaid for trying to sell me an Optima battery (D51 yellow). Local distributor wants $260 at "wholesale" for it. Bernard was going to sell it to me for just under $200 plus shipping. Problem was shipping was $77! So no go there.
This forced me to search some more.
You don't -need- a deep cycle battery (which the yellow top is) in a Prius unless you constantly make mistakes leaving doors open or unlatched or lights on. So if you don't (I have never fully discharged Pearl's 12V battery) a red top Optima would be fine. Walmart in Canada sell two different sizes of red top for about $200. But not the D51 (which is slightly smaller). Ditto for a few other suppliers (who were more expensive but still not bad). Sooo....

Now, a word of warning to those who might be tempted to emulate what I did. This is what -I- did and I take responsibility for that only. What you do is -your- responsibility. OK, with that in mind, read on!

Out to the garage to remove Pearl's 12V battery. It's not hard to do. I removed the negative terminal connection (to the body) first, as a slip of the wrench wouldn't harm anything. Then the positive terminal. Then the hybrid battery vent tube. Then the 12V battery vent tube (it just pulls out). Then the 12V battery hold-down bar. I had to pull hard on the relay assembly to release the plastic pin than holds it to the battery hold-down bar. The battery then was easy to lift out. Leaving the space shown in the first photo. Size is:
Overall 5 3/4" W x 11 1/2" L x 9 1/2" H
Inside tray 5 1/2" W x 9 3/4" L x 9 1/2" H
Stock battery in Pearl is:
4 13/16" W x 9 1/8" L x8 7/8" H (to top of terminals).

I took the battery into the basement to torture it.
Note the label on the top of the battery. I ignored it!
I peeled the label off and using a knife pried off the semi-transparent plastic cover revealing the battery fill holes. The caps just pull off.
WHAT A SURPRISE - no electrolyte covering the plates! Well, not really, it's what usually limits the life of a "sealed" battery. So I added distilled water using my patented technique, developed over years of motorcycle battery maintenance. I use a rubber tube, dip it in the water, cover the top end with my finger, and then put the other end over the fill hole and release. I get about 1/2 to 1 cc of water each time this way. Easy to control how much gets in each cell without dealing with surface tension and bubbles. I filled conservatively, stopping after the plates remained covered when the battery was tipped about 30 degrees.

Results? Well, using a high tech pulse load tester before this service it indicated the battery was at 40%. After service it now indicates the battery is at 70%.

I've include pictures of the battery mount place, the battery, the label, and the general area in the hatch.

Just a note for those who may panic when reconnecting the battery, I had to hit the "start" button an extra time to clear the "check engine" light before the engine would start.

 

If you look at the picture of the label the max. recommended charge current for the stock battery is just over 4 Amps.

I shortened my description of events as the post was getting rather long. I DID see liquid electrolyte in two cells. It was about to go below the plate level. This is why I was sure I needed to add water. In my experience the cells in the ends of the battery (this one and the motorcycle and car batteries I have worked on) tend to loose electrolyte faster than the centre cells. It appears to me the stock battery in Pearl at least, is a standard liquid electrolyte battery. This was confirmed several years ago when another member of the forum shook his battery and it "sloshed".

I kind of skipped over the reassembly. I rinsed out the "cavity" in which the fill holes reside. This is also the gas escape channel, leading to the gas escape tube you plug into the battery when you install it in the car. Then I put the plastic piece back on. It takes a bit of pressure to make it "snap" into the groves that hold it in place. Then I replaced the label, as it seals the top of the battery (the gap around the gas escape channel). Then I carefully wiped down the whole battery. It was then ready for re-installation in the car. Usually, if you get sulfuric acid electrolyte on the outside of the battery or on your "rags", you can smell it. I didn't detect any.

After I added the water, but before I re-sealed the battery (caps still off) I connected it to my regulated power supply. It puts out up to 2.5 Amp and I set the voltage initially to 13.8 across the battery. The charge current was at 2.5 Amps for a few minutes, then dropped to around 1 Amp for about 20-30 minutes. Then it dropped to about 1/2 Amp. I tested the battery at this point and got the 70% reading. I then raised the voltage to drive the full 2.5 Amps into the battery (I was trying to "stir" the electrolyte with the bubbles generated by "high" charge rates, as it is semi-trapped in the matting on each side of the plates). After about 5 minutes I reduced the voltage back to 13.8 across the battery terminals, and after a few hours the charge current dropped to 100 mA. At that time I re-sealed the battery and re-installed it in the car, after one final test. The final test result was the same as the one taken shortly after adding the water and giving it an initial charge - 70%.

My experience with other lead-acid batteries tells me this one will last another few years. It's now 4 years two months old (after the car was put into service). Probably a month or two extra as it was shipped and sat in a lot waiting for me.

One final comment. Comparing the measurements I posted with the size of the Optima batteries the D51 is the only one that will fit in the Prius in the stock location. Though I'm tempted by the new 6V ones they offer. Hmmm, one in the stock location, and another elsewhere in series. Hmm, 50 A-Hrs of battery. Hmmm....

I'll keep this thread up-to-date with how it works. Winter is coming!

 

The battery is in the rear of the car under the hatch area floor on the passenger side. Remove floor, remove cargo container, remove floor piece on the passenger side, then you can see it.

You can get a "battery tender" to keep charge in the battery, but if it is short on electrolyte (water, actually), then it isn't going to help a lot. It will just hasten the loss of water (water will be lost when it's charging).

In my experience, winter doesn't have a big effect on whether the car will start or not. The 12V battery is only starting up the electronics with a 50 Amp 1/2 second pulse. The engine is actually started by the 200V "traction battery".

I finally got around to calling a Toyota dealer here and asking how much for a new "stock" battery. I was quoted $219.40 plus installation. The Optima eLearnaid sells is about that in the US delivered, and in Canada, it "lists" for $400. The FIRST gold-acid battery I've ever heard about!

 

To "jump start" the car or to recharge the battery, open the hood. On the right, as you face the open engine compartment, you will see a largish black box by the fender - the "fuse box". Open this (the latch is at the front) and you will see a red plastic device you can flip up. That is the "boost terminal" under it. If you purchase a battery tender you can connect the "pig tail" lead there, either the one with the ring terminals or the clip one. I installed the pig tail with the ring terminals there (the positive one I placed on the bolt that connects the boost terminal, the negative one I placed on the bolt above the fuse box on the firewall). There is enough room to route the wires out of the fusebox and keep it water resistant.

You want to be careful what you connect to the Prius. There is a lot of expensive electronics in the Prius, much of it always connected to the 12V buss. So no cheap electrically noisy chargers! And as seilerts posted above, no high current chargers!
Do use a voltmeter to ensure you don't put too much voltage into the car. I wouldn't allow more than 15V. DO ensure you don't reverse polarize when connecting!!! Positive to positive. Negative to chassis.

A good rule of thumb is motorcycle or maintenance chargers are probably suitable. Rapid rate car or truck chargers are not.