TPMS battery replacement

Have 4x TPMS from my 2011 Prius from replacement 2 years ago (1 died) Kept them and recently helping a foreign exchange college student maintaining her 08 Lexus RX350 @ 212k miles with the 2GR-FE engine. Car has 3 older sensors (including the spare) and 1 died. 2 others were replaced by tire shop.

New sensors are Denso 550-0103 ($41 on Amazon, $37+ship on rockauto) These were the replacement I purchased for my Prius. Exact match. Made by Pacific Industries just like the OEM. Costco programmed my new ones but I could have done it with Techstream as well.

Trying to save the student some $ so decided to look into battery replacement. Here is the info so far

Digging out the old battery

After prying the rear cover off. Scraped off some sealant and liberated the battery. Need a thin blade (like exacto knife) to separate the battery from the welded on tabs.

Many people just solder the new battery tab onto the old tab. I wanted to see how difficult to remove the old tab to leave a nice hole to solder new battery tab to. Gobs of solder need to be wicked off the old tab. Tabs also insert from the bottom of the board so clipped off tab extruding from top of the board. Wife held the TPMS, apply flux, solder and pull with needle nose to liberate the tabs from bottom of the board. Tiny surface mount components are not too far behind (even got a tiny ball of solder on one) so need to be careful.



Replacements

Exact replacement on Mouser (Digikey required min 200 quantity) for $4+ and $9 ship. These Panasonic batteries are due to obsolete on 6/30/26

https://www.mouser.com/ProductDetail/658-BR-2450A-FJN
https://4donline.ihs.com/images/VipMasterIC/IC/PANA/PANA-S-A0006259314/PANA-S-A0008380763-1.pdf?hkey=CECEF36DEECDED6468708AAF2E19C0C6

TPMS casing has molded ridges and tabs that clips onto this exact battery. Another 2450 (24.5mm) likely won't clip in perfectly and more reliant on sealant for structural support.

Replacement battery tabs inserts from the top of the board which makes it easy to solder on. Tab length and measured distance on the TPMS seems to be a perfect fit (see drawing on mouser link and measured distance in pic)



On the mouser battery mechanical drawing, top left is looking from bottom of battery and top right is from top. So the polarity of the tabs are correctly matched to the TPMS board battery tab holes.

Weight

Weight is quite close. Lightest stick-on wheel balance weight segment is 1/4oz so should be no problem leaving the black backing plastic off (new ones I bought didn't have them. Just transparent sealant) I'd prefer not to reinsert the plastic plate back onto a compromised lock on the TPMS shell and worry about them coming off. I guess certainly can melt the lock once back plate is on. But seems unnecessary as new ones don't have the backing plate.



Results

Need to order replacement battery. Will report back.

A lot of work but save ~$40 x 4 or 5 for cars that have a spare. A key challenge is unless you know the exact battery shape and how it's held in the shell, can't order in advance. I suppose other 2450 lithium batteries with tabs can work. It would probably depend more on the sealant for structural support rather than just moisture seal.

Since the Panasonic BR-2450A/FJN battery is becoming obsolete. Maybe the new compatible Denso TPMS might have slightly different battery clip shape under the sealant to fit newer batteries. Just speculating.

 

Glad to hear counterfeits are working so well I assume it registered to the car with Techstream just like OEM?

Recently posted this on genuine Pacific Industries TPMS and copycats

fake TPMS sensors how to spot | PriusChat

I didn't take a pic of the genuine Denso/Pacific Industry replacement with the clear sealant but online pics show the circuit board patterns are different (close but different) My OEM and genuine Denso didn't have the CMIT markings.

Beside battery quality, I also wonder if there are differences in power consumption. Whatever the main chip is have probably have all the power saving smarts whether its no motion ultra low power, variable transmission rates, higher quality lower power consumption chip manufacturing process. Would be interesting to dig out the board and see the chip manufacturer.

Would be nice if there was a more reputable distributor for the none OEM so likely higher grade manufacturer. As noted in the linked post, Chinese manufacturing has many quality grades and prices for what appears exactly the same... But with subtle differences (sometime not so subtle). I purchase replacement iPhone batteries from a distributor for repair shops that are much higher quality than the ebay/amazon parts which even have the apple logo and prints identically. But these are always far less capacity than advertised. Also did some manufacturing sourcing in China and found coastal manufacturers more capable (and a little pricier) than those further inland.

But distributing copies require the OEM manufacturer not seeking legal action. Not legally effective to catch scattered small ebay/amazon sellers. A bigger more reputable distributor would need to assumes some risk.

 

Here is some more info on the Denso/Pacific Industry unit. Here is a tear down and shows the board side. Battery + mounting structure looks identical to mine so my board design is likely exactly same as this

I have some chip fabrication background expertise and looked up Pacific Industries website's TPMS info. Here is an interesting block diagram

Technologies | TPMS Products | Technologies & Products | Pacific Industrial Co., Ltd.

Without going into ton of detail. Accelerometer on a chip is designed and fabricated on MEMs (Micro Electro Mechanical) technology and computer chip parts (logic, RAM, ROM etc) are in CMOS logic. MEMs got invented because engineers figured out how to use older chip fabs to build tiny mechanical structures that responds to inertial and vibration and measure the changes. Hence miniaturized accelerometer, gyroscope, microphones are all in MEMs these days. Combining MEMs and CMOS into single chip (shown in above diagram) has also been going on for a couple of decades. Adding high precision and low power MEMs features is actually an important way for many chip fabrication manufacturers to survive by making other useful products instead of competing with multiple $10B investments for bleeding edge computer chip fabrication.

I'm guessing Pacific Industry's Kita Ogaki plant is their own MEMs+CMOS factory.

Domestic bases | Corporate Information | Pacific Industrial Co., Ltd.

I'm guessing the clones are all from China. Chinese auto market (bigger than US now in volume) surely have domestic TPMS suppliers and also domestic chip designs. Chip fabrication source could be TSMC. TSMC is often noted for advanced Apple, AMD, nVidia CPU/GPU/APU/AI chips but they have much older fabrication facilities converted into MEMs 2+ decades ago and have integrated CMOS logic to build computers + MEMs structure on a single chip for awhile now. Chinese domestic chip fab may not have reached this level so probably using TSMC's MEMs+CMOS logic capability. Just a guess.

Finally, whenever I've looked at high precision, high efficiency designs especially when involving high quality materials. German/Swiss/Japanese always lead the pack (Best bearings in the world are German/Swiss SKF, Boeing/Airbus use carbon fiber from Toray, a Japanese textile company that switched to carbon fiber when textiles shifted to cheaper Asian labor force, bunch of invisible high precision analog popcorn parts inside iPhones are Kyocera, TDK, Rohm, Murata etc. All high precision Japanese specialized manufacturers). I'm guessing Pacific Industries TPMS chip is probably more power efficient than the clone's Chinese designed chips. Again, really just a guess Tearing down a clone to take a look at its chip would be revealing.

In summary, I would guess battery is not the only difference for longevity.

 

Yes indeed, it depends on who is controlling the input materials, design, and output QC. In case of apple, they control the input materials (lots of chips not from China) manufacturing specs and output QC. Where Chinese domestic controls these, 10 grades usually appear from simple components to even at the level of a car haha.

Often the 10 grades just start with stripping parts from the highest grade. Even simple stuff like a $10+ USB to serial communication port (CH341A dongle to flash EEPROMs) there are multiple grades. Cheapest one require a solder mods to even make it work but cost $2 haha.

 

Regarding rechargeable, self charging etc. Looking at the design, its quite clear objective #1 is moisture seal, reliability, and longevity.

• Biggest challenge to access the battery is scraping away all that sealant for moisture seal. One could rubber gasket, screw or clip on the shell but will cost more and be more failure prone then pouring down sealant.
• A non replaceable battery have solid ultrasonic welded tabs on the battery and tabs soldered to the board. If it was spring loaded changeable coin cell, contact reliability variable comes into play in a high vibration and inertia abusive environment.
• Lithium ion rechargeable battery requires a BMS and need to moisture seal the rechargeable port.
• Self generated charge probably require 1) a rechargeable system to provide power when unable to charge 2) need self charging mechanism. Automatic watch mechanism are quite complex. I wonder what low cost mechanisms exist?

Most home electronics don't have to deal with this abusive environment.

Anyway, Toyota is making hey @ $100+ if a distributor like Denso can sell it for $40+. Pacific Industry probably can't have much more than $5 worth of component cost before all the downstream cost to distributor.