Optima - Toyota Prius 12 Volt Auxiliary Battery Installer

I only had the OE battery out of my '04 Prius a couple of times. I didn't investigate the cover, but it was clearly evident that there was free acid sloshing around inside the battery

Toyota does interesting things with their batteries. For example, on my '07 FJ the Panasonic OE battery had a raised ridge on top with "maintenance free" sticker across it.

Peel off that useless sticker, and lo and behold, caps to remove. I did this in 2008 and was surprised to discover the liquid level barely above the mat. Used distilled water to raise the liquid level to where it should be: a meniscus distortion where the liquid level touches the plastic projection at the bottom of each "well" in the cell

Anyway, don't forget to fully charge the new battery before installation

 

I'm happy to see you found out what I've been saying all along! They do indeed have fiberglass mats, but they are not starved. Basically you just lose the "A" but I'm not sure anyone wants to call it a "GM" battery. VRLA is more accurate.

Toyota erroneously refers to it as an AGM battery type which it clearly is not by definition. I think Hobbit was the first one to discover this.

You are only seeing .01A? I suspect your ammeter is not accurate. I see more than this on my 2008 w/ Smartkey on. (no cabin lights)

Are you sure that battery isn't effectively the same as the Prius battery? Does it have a translucent or a black case? They seem to mix them up, though most of the newer ones I keep seeing are all opaque black. Maybe they don't want to have people object that they are supposedly selling an AGM/Starved Electrolyte battery but then it's flooded.

Actually I would surmise the HiHy has a larger EPS motor and thus can pull more peak amps. Does it also have the high-current PTC heaters like the Prius?

 

They cannot deny your warranty because you do not buy their battery. The battery is specifically excluded from any warranty in any event!

It's a glass-mat valve-regulated Lead-Calcium battery. It is *not* starved electrolyte. The charge voltage curves are the same for all lead-calcium types, but you have to be careful about overcharge in any kind of starved electrolyte system, as any electrolysis that results in venting will destroy the battery. (water loss)

Toyota's paranoid warnings are not real. You can run any type of 12v lead-calcium battery, including a "normal" car battery without any problems, but fit and lifetime are not necessarily going to be the same.

The biggest reason these batteries fail so soon is lack of a proper 3-stage charge algorithm. They are treating them just like a standard car with an alternator does, (float) so they last no longer than a standard car battery does.

 

"Maintenance free" does not mean that they will not ever lose water, if they are overcharged too much (or charged with too high/non-temp-comp voltages) they will electrolysize and if this exceeds the ability of the calcium recombinant cycle, then they will pop the valves and vent resulting in water loss. Maintenance Free means they are lead-calcium and normally will recombine instead of losing water. For instance a non-recombinant golf-cart type battery loses water with every charge, and thus must be maintained often. This is how car batteries used to be, so it was common for a service station to top off your battery with a fill-up.

 

When the Prius is IG-OFF and the doors and hatch are closed, what quiescent current drain do you measure?

Highlander Hybrid also has PTC electric heaters, for the same reason as Prius.

The HiHy original equipment battery has a translucent white case, standard sized terminals, and the terminal polarity is reversed compared to the 2G/3G Prius. The manufacturer is Furukawa Battery and the battery is made in Japan.

I took it out of the HiHy last winter as a preventive maintenance move when I bought a TrueStart replacement made in Mexico, priced at $96 (plus tax) from the local Toyota dealer. The replacement battery has a label asserting an 84 month warranty.

Since then the original HiHy battery has been sitting on the garage floor and I've attached the charger periodically to it. I recently removed the seals over the battery caps and topped off the electrolyte with distilled water. After fully charging that battery and waiting overnight, the voltage is ~12.5V so it still has some remaining life.

I carried that battery and jumper cables in the 2007 Prius the other day while driving around, since I knew the Prius battery was close to dead.

 

Some like the AC Delco batteries are truly sealed. Others that claim to be clearly are not, and one should inspect yearly to ensure the liquid level is proper

With regular use of the VDC Battery Minder, I have batteries on seasonal equipment approaching 7 years old that still have a 13.1 reading after 3 days resting

 

FYI, there is a temperature/voltage coefficient for Lead acid. Somewhere I have a good chart but this will have to do:



Here's another:



This basically means if you are trying to determine SOC from resting voltage, you have to take into account temperature.

 

The new battery was manufactured on August 25, 2010 and shipped to my dealer on December 1, 2010. I bought it today for MSRP of $138.70 plus sales tax. The open-circuit voltage out of the box was 12.9V. See photos.

I also attached a photo showing quiescent current draw (~10 mA) with the car IG-OFF, doors and hatch closed (but hood open.) The 12V battery was disconnected.

I shook the new battery but did not hear any fluid within.

 

Nice. This is a fresh unit with a decent price. I'm duly impressed!

Can you take that nice Fluke 87 and put it in current mode (preferably on the 400ma scale) can measure again? I've never seen a Prius this low. The lab supply clearly only has a .1A resolution, so it might be off a bit.

Of course, that doesn't mean there isn't liquid, just that it isn't sloshing (maybe very full?) or you simply can't hear it.

 

The temperature varied between 20-23 C

 

When the Prius is IG-OFF, with doors and hatch locked, the current drain fluctuates rapidly, ranging from 16 - 25 mA.

I used the A input, but the meter readout is in mA. I did not use the 400 mA input since I did not want to run the risk of exceeding that current value as doors are locked/unlocked or if the brake accumulator pump decided to run while the measurements were being taken.

A Canadian member e-mailed me today, asking me to mention the sheet metal screw that secures the traction battery vent to the fender. That screw is not easy to replace, with the hatch trim immediately above and the battery below. When replacing the 12V battery, that member dropped the screw into the fender. I did the same when installing my new battery last night. Fortunately I have a magnetized wand which is great for picking up loose hardware.

My correspondent's solution was to use a piece of gum to hold the screw to the socket. My solution was to use the wand to magnetize the screw so that it would stick to the socket long enough to get the screw started in the hole.

 

Ok, that sounds a bit more reasonable and closer to my readings. On my 2008 with doors locked and factory security enabled I saw 29.82 ma average over the course of about 5 minutes. I used my calibrated Fluke 45 bench meter to make the readings. I had smartkey on, but the key kept away from the car and all doors closed overnight before my tests. It's very dynamic; dropping as low as 18, with short peaks into 55ma. The blinking security LED adds 20ma alone when it's on! Right now I've got slightly more than this in my car, as I have some add-ons, but I had all this disabled during my first test. Still, 30ma is more than most cars!

I don't know what the rated capacity of the OEM battery is, but I'd guess about 30ah based on size. Assuming this, with a totally healthy battery, that means in less than 42 days your battery would be absolutely toast. Now of course we know the Prius will do a no-ready even before the battery is totally flat, so with that in mind, I'd give it a month until you can't make it ready w/o a jump. Now shutting smartkey off (which it does automatically after a few weeks anyway, right?) will probably offset this by a couple of weeks, so you'll probably get a month and a half.

I've added a switch-mode charger to the 12v system that is enabled whenever the car is plugged in for PHEV charging. It keeps the system at 13.8v as long as there's power. I have a block heater coming that will also tie into this, I'm going to build a circuit that automatically adds a series diode to the block heater feed when the car is plugged into 240v, but is bypassed on 120v.

 

The battery capacity is in the mid-30 Ah range. I understand that the battery should not be discharged to more than 50% if you desire to promote battery longevity, so this implies ~18 Ah to work with, assuming that the battery is 100% charged to begin with.

18 Ah / (24 hours / day x 0.02 A average current draw) = 37 days.

In your case, the average current draw appears to be 0.03 A, so you would have 25 days.

Of course, as the battery ages its capacity diminishes so the amount of time that the car can be parked will correspondingly decrease.

Toyota recommends that the 12V battery should be disconnected if the car is going to be stored more than 10 days (TSB PG007-03).

 

Thanks for uncovering the AH!

I think your amp figures are conservative. Because you used the 10A scale, you can only expect +/- .5% accuracy. (that's 50ma!) Mine was done with a 100ma shunt with a +/- .05% accuracy. Try it again on your 400ma scale if you want more accuracy. You can hit the brake slightly a few times just until the pump comes on then the accumulator will be fully charged and there is little danger of the pump coming on and blowing your meter scale.

The easiest way to do this is in the back, first trigger the hatch latch mechanism manually so the car "thinks" it's shut, then shove one probe in the white B+ connector and then clip the other directly onto the + battery terminal. Then, once the car has "went to sleep" you can just unplug the B+ connector and all current will be running through the meter. I didn't pop my 100ma fuse in 5 minutes, so your 400ma scale is going to likely be fine.

On the 87, fluke contends the 400ma scale has +/- .2% accuracy, (.8 ma) so you'll get a more accurate reading.

 

I just recently replaced the original 2004 Prius battery with 198,000 miles on it. Do do what I did, I left the vent plug on the original battery when I took it in. So I had to buy a replacement vent drain kit for 8 bucks. Another silly thing i did was close the hatch after taking the dead battery out. 6-7 years of life for a $150 dollar battery is not so bad.
It is pricey, cost about as much as the battery for my bmw 330i(which is about 2x the size & also located in the trunk). One thing you should do is go online and check the local dealers for coupons. There is almost a good chance a local shop will have 10% off parts.

 

Since you raised the question of measurement accuracy, I connected my DC power supply to a 500 ohm resistor (two 1K ohm resistors in parallel) and used the Fluke to measure current at different voltages.

At ~25V for example, I measure 50.0 mA when using the mA input. The readout becomes 50 mA when using the A input.

I repeated this exercise at 20, 15, 10 and 5V and the current measurements went down proportionately, 40 mA down to 10 mA. I switched between mA to A inputs, at each voltage level.

I conclude there's no difference in measurement accuracy when using the Fluke's mA vs. A input, except that the readout shows 0.1 mA precision when using the mA input. Therefore, I would say that my current measurements accurately reflect the quiescent current draw of my 2007 (which is not necessarily representative of other Prius, depending upon option mix, aftermarket accessories etc.)

 

This is a good test, I too conclude your meter is surprisingly accurate. What I'm wondering now is why I have such a higher reading? I have a 2008, with smarkey, factory alarm enabled, but no nav, and when measured all aftermarket accessories and modifications disconnected.

If there's anyone else similarly equipped to make a quiescent current measurement, I'd be interested in seeing your results.

These results may give us information on why some people have more trouble with the 12v battery than others. With Patrick's being so low, I'd assume he's pretty safe.

 

My car does not have a "factory alarm", at least I am not aware of the presence of such.

Hobbit measured 11 mA here:
http://www.techno-fandom.org/~hobbit/cars/prius-12V/

However his 2004 is a base model without Smart Entry / Smart Start, and he did not mention the quiescent current pulsing up & down. Note that his car has the small GS battery with translucent case, similar in size to the Classic original equipment GS battery and rated 28 Ah.

 

Good point, Could be the security.

The pulsing is likely the Smart key system sending out it's 134.2khz interrogation signal.

All cars have the Alarm functionality, which can be enabled/disabled via TechStream. You can optionally add the Glass Break detector and extra horn, as all cars are pre-wired, but even without, the horn will honk and lights flash if someone opens a door without a "proper" unlock.

The Toyota "glass break" detector plugs into a 3 pin connector located on the upper left side of the lower middle dash cover. You can make any type of aftermarket detector work that will provide a ground to the trigger wire and release upon detection of vibration or intrusion.

The auxiliary security horn is similar to a stock horn and uses the same 1/4" spade connector. The connector is taped to the wiring harness that sits on the right side frame rail near the shock tower.

I have added the horn, but not the detector. (yet) It's highly probable that simply enabling the system causes more current draw.