DIY report: replace 12v battery with 55ah "ExpertPower" from Ebay

I contacted ExpertPower.us asking how I can expand the vent on this battery, and their response was... "Our batteries aren’t designed for automobiles. The cold cranking amps of the battery is not strong enough for a car, and the battery is meant to be fully drained and then recharged after use. We advise not to use it for your application."

Apparently, the 12v battery does not crank the engine. Proof of this is my very old/weak 12v battery has lasted another year, even though it got drained at least 6 times this year. It was so weak, it would drain down to 12.0v from 12.7 in just one minute of bleeding a brake line (with the brake lights on).

Regarding the gas given off by AGM batteries, I came across this... "Even though AGM batteries are considered to be maintenance-free, they still require venting. If you overcharge the battery, charge it too quickly, or don't allow enough AGM battery ventilation for the absorption mat to keep up with, the same dangerous build-up of hydrogen gas can occur".

To be on the safe side, I decided to vent the AGM battery gases beneath the trunk, through the hole provided.

The battery warranty is the least of my concern. Thanks for the suggestion. We'll see how it works out.

 

Lol... Sounds like ExpertPower isn't actually an expert... Only job a 12v Prius battery has is to turn on some relays and the lights and computers. And as our decade long debate continues, we can all mostly agree that the need for venting is solely to prevent poisonous gasses from entering the inside of the car during thermal runaway because the 12v battery got too much charge.

Thankfully, the amount of charge Toyota sends to the 12v is pathetic... As in you'd have to drive your car for more than 12 hours to entirely charge your 12v battery and in non-hybrid cars an alternator will charge your battery way, way faster than that.

As in VW with a battery inside the cabin are massively more prone to thermal runaway and poisonous gas release and since the 1930's there's no evdence that's ever been a problem.

 

I decided to pry up the plastic top, to see what damage I have done. It turns out that I did drill down into one of the cells. The damage inside the cell itself may (or may not) cause problems. The voltage is good, so I don't think the cell has been shorted. I plan to glue a plug into the hole that I drilled into one of the cells.

Here is what it looks like under the top cover. The little vent valve goes into a circle underneath.



If you wish to drill a hole from the top, you could center it over the circle that the little vent hole feeds into. This center of this circle is 15mm from the side edge and 14mm from the outside edge.



The best approach my not to drill at all, and instead try to capture the gases that escape through the little vent hole. 20/20 hindsight, I think that is what I would do.

 

This is the first time we've seen underneath it... Do you think that the circle where the vent hose fits into is significantly thinner plastic so if the battery has to vent it would blow through the plastic at that point? That's always been the theory, but has not been verified.

 

Each cell has a rubber cap that is in the center of a circle. The top has a circle that would fit into the larger circle of each cell. The tiny vent enters a circle as well that would fit into a circle as well. If there is pressure anywhere, it would feed through the canals, from cell to cell, and then to the circle where the vent is, which has a canal to one of the cells. The tiny hole, about the diameter of a pin is always open. So the gases will vent from the tops of each of the cells, and then out the tiny vent.



I cut the old vent value into two pieces.



I cut the new vent valve from the top, and trimmed the old vent valve so that it would be kind-of flush with the top. I plugged the hole in the plastic top, and getting ready to glue a piece of rubber on top of what you see here. It will not pull out, and I can attach a vent tube to it.

 

I am constantly amazed at what humans will do to save a couple dollars....

 

Me too. Going forward, I may pay $255 + tax ($275) for an Interstate battery for a 2008 Prius instead of the $136 that I paid for the battery on Ebay. It is a lot of trouble to install this battery safely (because the Ebay battery does not make it easy to vent the battery). Also, the posts are different and the battery is about 1.75" taller. But it has more amp hours, and may actually last longer (we'll see). But I am done now with this alternative... live and learn. Still, $275 seems excessive for a small car battery that has a warranty of just 3 years.

 

have you called around for oem prices?

battery-12v-0054421171325

 

It seems to be a widely held misunderstanding. The length of the warranty is not the same thing as the lifespan of a part nor is it indicadive of lifespan. Warranty is based on the statistical likelyhood a manufacturing defect will reveal itself. That relates to quality control. Lifespan is dictated by the design parameters and maintenance after installation.

The only 12 V battery I have ever changed in 17 years of ownership was at around the 10 year mark and I did nothing special to achieve that. The replacement is still going strong. Every ten years is good enough for me at a cost of $27.50 a year.

 

Here is my final installation. On the positive post, I added a nut underneath the positive cable connector which has a larger diameter than the bolt that passes through it, allowing the bolt to be tightened freely. On the negative terminal, I cut the thread from a bolt and inserted it into the battery terminal, allowing the negative connector to be attached using the original nut. There is a rubber cap holding down the ventilation hose nib, and the silicone is still drying in this pic. Another, easier strategy, is to use a 1/4" drill bit and drill 3 mm into the existing vent (from the upper side of the battery), and glue a "1/4 inch Plastic Hose Barb" (from Amazon) into the hole. With this strategy, you can vent the battery into the hole in the bottom of the trunk.



I tested to see if the battery vents. Most of the time, the battery showed no sign of venting, other than I noticed it vented a little bit into the finger of a rubber glove, when I allowed my battery charger to perform a "recondition" step, which applied a charge of 14.37 volts. The battery will vent hydrogen gas, which is 14 times lighter than air. I feel safer to vent it out beneath the trunk. Since the battery does not vent much, maybe venting is not needed (your decision).

 

For another $50 you could have bought the proper battery from NAPA or Walmart.....

 

How long have you had the battery for? Still going strong?

The capacity of my expert power battery went down from 25Ah or so (from full charge to 12V) to about 12AH in about a year. Admittedly, I did not drive the car lot but was sure to start it at least once a month.

Considering getting another and keeping it on a tender more often.

 

Periodic recharging with a legitimate smart charger that goes up to 10amps is essential for a Prius. Do that a couple few times a year and you'll be like me who's gotten more than 9 years out of my last 55amp-hour expert power battery.

 

Yes, finally! Metal spacers are the way to go in this situation. Earlier in the thread there is a shot of the hold down floating in the air hanging off a long bolt which is mostly up in the air. That is very weak. Put a solid metal spacer between the bolt head and the deck as for this positive post. Then the bolt can be tightened down which makes the spacer, essentially, an extension of the deck and quite strong.

Also why does everybody insist on mangling the negative battery cable? Buy or make a new one with loops on each end and then it will bolt down just as firmly at the negative post as the other end attaches to the body of the car.

An AGM battery is below its gassing voltage at 14.1V at 25C. As you have demonstrated. The bigger problem is that the gassing voltage is below 14.1V at 40C, and the car does nothing to compensate for this. Which is why, I suspect, the OEM battery in my car is so light and has so little capacity. We have weeks and weeks where the temperature when the car is driven is never below 100F, the car is designed for a more temperate climate, and it dries out the battery. The gassing should only occur once the battery is fully charged though. Keep the SOC below 100 and it won't dry out. Instead it will sulfate. There is no free lunch.

Oddity with 12V battery voltage measurements andtranmission | Page 2 | PriusChat