Replacement button cells for Active Pen

I got a PN556W Active Pen with my Latitude 5285.  But it seems to have died.  I have replaced the AAAA battery in it to no effect.  I was able to track down a working one and borrowed the AAAA battery to no effect.  But when I borrowed the coin cell batteries it worked.  So it looks like I need new coin cell batteries for my pen.  The part information I was able to get from Dell is NTM35 BTRY,RSRV,3V,COIN,LITH,E4 But any time I search for it I get a replacement motherboard cell, not anything that would fit in my pen.

Does anyone know what coin cell battery I need?