I think you might be out of luck, It seems to have first been released in 2010.
Have you tried emailing Skil (or Bosch) directly?
They may have old stock (or not), or may be able to recommend a part from a newer machine that is compatible.
My quick Google search suggests that the batteries were discontinued in 2018. Unless you are willing to pay to have the batteries rebuilt, it might be prudent to bin it, sorry.
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