A friend of a friend of mine has a prosthetic knee that was developed in 2010 which requires battery packs that are being phased out. He has asked me if there is a way to replace the internal batteries for these units, so I cracked one open and they seem to be an array of about 12 x 3.7v lithium ion batteries arranged in two parallel "strings", each of 6 cells in series (6S2P) (approx nominally 22V per cluster) of the following type link . These cells individually are not available for anything less than 10,000 unit purchases, which obviously is not really an option for this one off repair. I am a computer engineer with some experience in power systems but I have never worked with a lithium ion source before and am trying to be cautious about choosing an appropriate replacement battery.
I have been looking at these two batteries as replacements. Each vary a little bit from the source battery, either in size, capacity, or discharge rate. What I am curious as to is whether these variances from the original pose any significant risk? I suspect the power characteristics are close enough to provide at least ... some functionality, however the charging circuit and battery packs are pretty elaborate and I would hate to drop $150 in battery cells just to find out that they didn't work or worse... caused a safety issue.
If it's of any interest, here is the link to the product that this comes from Power Knee
If there are resources as to answers for these questions, or links to other battery suppliers who may be able to meet my requirements, I would accept any and all feedback. Thank you in advance.