Found it! Ramtron FM1608

[James]

Anybody have any of these spare that they may have bought in extra from China? My SS has factory reset issues, so may as well get shot of the batteries and socket one of these in.

I bought a load of MC6821PIA's in actually, so maybe a trade to be had? Installed one on LaserBall and all worked fine, think I have another 7...

 

[Paul]

Unfortunately havent got any, however cheapest i can find is, as you say, in From China... 10 for £21-ish

https://www.ebay.co.uk/itm/172481002515

Or the cheapest in the UK seems to be Littlediode (again!) at £11.99 OBO

https://www.ebay.co.uk/itm/162684978439

Take your pick