HP 28S is very loud when opening/closing

[edryer]

yes, thank you Burkhard, I did indeed mean your suggested 2/3 AAA, flat-top, apparently there are two types of flat top and one of them isn't truly flat top, your link was to the smaller (and suitable battery) - if any folk order these (other from burkhards link) and they are described as flat top I suggest looking to make sure they are truly the flat top variety (also known as Industrial in some places).

I have also seen 1/3 AAA batteries advertised, coupled with some dowel and aluminium foil this may also be a solution. One guy used 3 watch cells and dowel + aluminium (+ custom cover (http://mpshp.com/hp28s/Foto01.jpg) ) but 3 x 1/3 AAA may last quite a bit longer.

So another idea may be 3 x 1/3 AAA with dowel/aluminium foil which may truly relieve all pressure on the battery hatch!

The 28S is a fantastic device, and I note now that prices have risen the last few years, becoming far more collectable.