Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
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?)
They *all* don't work? and after only 5 months?
I would think they need the batteries changed, if it was only the non-solar ones.
I myself stored away a solar calculator, a cheap one, in the '80s, for a while, and it still worked after some months or a year or two.
Pressing the C button and holding it down for a few seconds might help, or it might not.
If there is a pinhole in the underside of any of these calculators, try straightening a paperclip and pushing the button hidden inside the pinhole and holding it for a few seconds. That might straighten them out... though *why* they would be defective is hard to see. Were they stored in dim light? that might disorder a solar calculator, some.
If any were non-solar, and had a battery that leaked, it might be that the battery terminals are corroded and need cleaning. If that appears to be the case, let me know and I will instruct you how to clean the battery terminals in the calculator properly.