I picked up McMurdo Smartfind S20 units before leaving for Mexico in 2016. The batteries in these units have a seven year life span which meant they expired in 2023, but I decided to disassembled one and checked the voltage.
The battery pack had s lithium manganese dioxide (li-mno2) battery which is good for applications with long-life requirements. Reviewing datasheets there is a less than 1% capacity loss rate / year so at 8 years (without setting off the unit), my unit it should still be at 92% charge.
Checking the voltage I found it to be 6.52V compared to a 100% charge of 6.6V. Reviewing datasheets I found that with 30% power remaining the voltage would be around 5.7V which gives me great confidence that my battery is still very healthy and not in need of replacement. I’ll wait until it reaches 6V before replacing (roughly 75% charge). Make your own decisions since this is a lifesaving device.
Interested in changing your battery? I found a few websites that sold replacement batteries by searching for 91-156D (P/N on the battery pack). The SOBOUR Battery made in China came up a few times and I decided to order one for testing. The pictures below show the disassembly process.
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