Why do you use File::Copy? I tested your code and, to my surprise, copy does append to a file if you open it for appending and copy to the filehandle.

copy "file1", $fh
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But it's not documented in the POD, and it only works as a side effect of how File::Copy deals with filehandles. Why not do as others have suggested:

if (true) {
    open (my $fh, ">> RESULT_LOG");
    open BATTERY, "<Battery_Status";
    print $fh <BATTERY>;
    close BATTERY;
}
else {print "Error"}
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It's a couple of extra lines, but you can use all built-ins, obviating the need for an external module.

My two cents.

--marmot