We are now designing an adaptor to put two AAA batteries in a Spice machine. The Spices were the HP32E, HP33E, HP33c, HP37E and the HP34C - the top of the series.
The Spice machines were designed as low cost compared with the HP65-HP67 series, and as replacement of the Woodstock series. In opinion of many HP experts, too many corners were cut to manufature them - several internal connections rely on pressure exerted by the screws that close the box - while in previous units the box screws did not have circuit integrity functions. Therefore, these machines have higher fatality rate than other models.
One of the issues that plague the HP Spice is the battery bay. The original rechargeable batteries wear down, but the problem for the replacement is that the normal AA size is 1-2 mm too long for the machine - and you break the machine in the medium term. Ignacio Sánchez suggested to design an adaptor that used two AAA batteries - where the size challenge does not exist.
(continuing with the story: after the Spice series, the lower range was inherited by the Voyager series - for many, the most perfect calculator design ever, with the HP12c and the HP15c as the main examples)