This is the third strike for APC in my book.  Their equipment has now failed me three times.  Three different models over the years have worked fine until the batteries were expended, then I buy replacements and the unit is trashed.  With the higher end XS900 I assumed it would be fine with the replacements, but the charging circuit is not working.  Batteries have been test and they are fine so I'm assuming APC designs products that won't survive the death of the first set of batteries. So these two new batteries go in the pile of perfectly functional batteries that have nothing to go in.