Tadiran (pronounced 'TADDY-ran') 3.6v 1/2AA Battery for the IIgs ROM3 or Mac.  These are NEW Lithium batteries, not New Old Stock (NOS) and have a date code printed on them for reference and proof of 'freshness'.

Can last 10 years or more in most computers!  Although we recommend they are changed every 5 years just to be safe and prevent and possible leaking and acid damage.