One of the issues with 2s, 3s, 4s, etc. battery packs is that as the pack discharges it's possible for one cell (the one that depletes quickest) to become reverse biased once its internal resistance reaches a high level. This is referenced specifically in IEC60086-4 (Safety standard for Lithium primary packs) but seems to apply to all packs. I have a fair few series NiCd packs which I still use but some have reduced capacity due to crystallization which I'd like to reform by low current deep discharge. The crystallization has not reached the point where the separators have been compromised as all cells in the packs can reach their correct terminal voltage when charged. Is there any reason why the application of reverse biased diodes across each cell in a n-series pack wouldn't protect NiCds from damage in the same way that it is implemented in Lithium based primary packs (thereby allowing me to do a deep discharge on a series pack rather than each cell individually)? Has anyone seen back-diodes present in rechargeable packs?
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A reverse diode will not protect below 0 V, only below -0.3 or -0.7 depending on technology, which is not enough, most Ni chemistries suffer damage below 0 V. – Neil_UK Apr 08 '22 at 11:32
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Thanks - a bit more digging around has revealed some data (albeit apocryphal) to suggest that small reverse bias on the cells is implicated in the formation of crystallization. – BlueTwin Apr 08 '22 at 11:45