The world was very different in 1996. It was a time before Facebook, Twitter and Spotify. Before the iPhone and International Space Station. And it was long before we started our Energizing IoT blog!

One thing that has not changed since 1996 is the quality of our batteries, and a 2016 discovery proved that to be the case.

Michel Guégan, a former Saft employee, found a number of batteries in a cupboard at the Saft Poitiers facility. Among them were LS 14500 batteries in a cupboard with a code date of 96.102 (or April 12, 1996). Ever inquisitive, he and colleagues set about testing the batteries to check their performance to see if they had held up over time.

The first test or ‘wake-up’ test, was to check the behavior of the batteries under pulses. This involved various tests including a dozen pulses of 80 mA for one second, with a rest of ten seconds between each pulse.

Mr. Guégan said, “Just like Sleeping Beauty, a single pulse was enough to wake the batteries up and from the second pulse they were responding with a voltage over 3 V. This was quite remarkable, bearing in mind they had been in storage for two decades or more.”

Such a long time in storage will have led to an increased influence of passivation in the batteries.

For liquid cathode systems, such as Lithium-Thionyl Chloride (particularly popular for IoT applications), the phenomenon of passivation is normal.

The formation of a solid passivation layer prevents further corrosion and, more importantly, avoids any internal short circuiting of the battery. This layer also protects the cells from discharge on their own and enables their long shelf-life. However, it reduces performance over time – particularly in the battery’s voltage response.

The longer a battery is in storage, the greater the passivation layer (and greater the impact of passivation). So, for these batteries to perform so well under testing is notable.

The second test was to measure the remaining capacity and the accumulated self-discharge.

The batteries were discharged under a constant current of 2 mA until full discharge (2 V). On average, the batteries still yielded over 90% of their original rated capacity – another remarkable outcome. Even after so long in storage, these batteries were still able to provide a near-same service as brand-new batteries could.

Mr. Guégan added, “I think some people can be a little skeptical about the durability of batteries. But this just goes to show that, even after two decades in storage, we manufactured high quality batteries with extraordinary lifespans. For them to lose virtually no energy in that time was really impressive.”

The second test displayed a completely normal discharge tray, a perfect end of discharge, and nearly 1000 h of discharge – an exceptional result after 20+ years in storage.