Tadiran lithium thionyl chloride batteries

Well my blog post about battery life caused a bit of a stir. My point was that you should be careful of claims that a Zigbee module will last for 10 years. I did point out that some automatic meter readers seem to be lasting a long time, but a concerned reader provided links to show that some utilities in Houston are having problems. I can see that the hotter and more humid your environment the harder it is to get long battery life. In the comments to my blog, EDN’s very own Margery Conner pointed out that Tadiran has some very cool lithium thionyl chloride batteries that do seem to exhibit 20 year life-spans. Indeed, Sol Jacobs, VP and general manager of Tadiran  wrote me and told me about Tadiran’s success with this chemistry. He sent a press release that describes how their PowerPlus batteries will soon come with end-of-life indication. They will indicate either 5% or 10% capacity left, depending on the model. This will allow users to only replace batteries that really need it. I looked over Tadiran’s website and was very impressed by their batteries. The cases are welded shut and there is a hermetic glass-frit seal that prevents corrosion. The greatest thing about Tadiran batteries is that you can buy them from distribution. Allied, Digikey, Jameco, Newark, and Mouser all carry Tadiran. I have not looked to see which ones carry the Power Plus ones with tabs like I want to play with, but I will figure that out soon enough.

These small non-rechargeable lithium thionyl chloride batteries have tremendous capacity and a relatively flat discharge curve. The TLM-1550HP can do 15-ampere pulses and 5-ampere discharge rates. The TLM-1550MP can do the same but has 800 mA-hr versus 550 mA-hr capacity. It took a while to figure out why the medium-power MP has more capacity than the high-power HP battery but looking at the datasheets for each one shows that the MP version does have less capacity at very high discharge rates. Now, a 1550 cell is 15mm by 50mm. That is the AA battery size. There are NiMH AA batteries that claim 2650 mAh. Remember, that is at 1.2 volts and that voltage sags to 0.9 over the discharge. The lithium thionyl chloride batteries Tadiran makes discharge from 4 to 3.25 volts. The differentiator is not just the higher voltage (that can power the electronics directly, removing a power converter inefficiency). The big deal about these batteries is the long shelf life.

Now all that being said there still is the systems design issue. I pointed out the difficulties of that in another blog post about my Maytag refrigerator. There, a Cherry switch failed catastrophically and caused my icemaker to spew cubes out onto the floor. My supposition was that the Cherry switch was just fine. The problem was that Maytag sealed it inside a rubber boot that held in moisture. I see the same issue here. Sol Jacobs is rightfully proud of Tadiran batteries. But if the system engineer does not do a great job, no battery will last 20 years. When I consulted to HP, one of the products we had problems with was a data-acquisition card with 10 megaohm impedances on the front end. The card worked just great— in the lab. But the customer was Fiat in Italy, and in that hot humid Italian climate, in a system that had a fan to drag all the icky garage air into the box, the cards would not stay accurate for more than a few months. If you had a Tadiran or any other battery on that board, you could not expect 20 years life. Sol and the other component makers would rightfully point to their lab data that showed 20 year life, but that implies you can control the environment as well as they did. Heat and humidity will kill any battery before it’s time. As an example I have posted a picture former EDN Editor in Chief and current contributor Steve Leibson sent me. He came from a systems-design background and he is skeptical of 20-year battery life as well. So don’t blame Tadiran if your batteries don’t last—you have to design the system to protect the batteries and eliminate all leakage paths and temperature extremes. Good luck.

This NiCd battery pack leaked at both ends. Tadiran’s batteries are welded and have a glass frit seal so they should not exhibit this problem.

And let’s cheer for former tech editor and current contributing editor Charles H. Small for the funniest (and most prescient) headline from 1994: “Batteries explode into new applications and new chemistries”. It’s still a great article, BTW. And here is EDN’s Margery Conner’s comment on Tadiran.