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I suggest that you remove the batteries, if any, all of them, from these calculators.
Leave them that way in a moderately warm, dry, dust-free quiet place, for at least 2 days.
Meanwhile examine the batteries, and dispose properly of any that appear old or leaky, for sure.
Solar cells don't 'recharge', by the way, unless the light source is very faint. A solar cell in outdoor light should immediately enable the calculator to be used - unless it is specifically designed to use rechargeable batteries. (?)
Have any of them been dropped or otherwise mishandled?
What maker and model #s are they? perhaps there is a reset button sequence applicable to their being inoperative after months of disuse. (Were any of them left On for that duration?)