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In the process of getting boat back in the water, Its been in dry dock for several years. Have done nothing with batterues. Voltaage on batteries fine. Just checked internal resistance on 5 cell battery and had one ceil with a high rating 20 ohm other 4 cells were between 5 ad 6. Does one high cell mean battery is no longer good.
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Yes, that means one cell is starting to degrade ahead of the others, and it will eventually drag the others down along with it as the "weakest link" in the chain applies here. On caveat could be a poor connection on the charger balance cable lead for that particular cell connection giving a false reading. This is easy to spot because the same cell number over different packs might always read higher than the others on the charger. Also, was the pack stored long term fully charged by any chance? This accelerates the chemical degradation of the pack and should never be done.
There is no one size fits all for good IR because IR is inversely proportional to capacity. A 2500 mAh pack cells will have double the IR of the exact same 5000 mAh pack cells, and this is normal. The 5-6 MO readings you are getting tell me its likely a 5000 mAh pack you have? Even if the IR isnt perfectly accurate (and most measured on a charger is not), its still great for establishing a baseline for the cells on a new pack to look for trends or outlier cells different from the rest of the group like you have
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