please advice an EE idiot on using chargers

[vaklaff]

Thanks to all the suggestions, including those I received privately.

A side note first, I'm not German but Czech (*). I'm not sure what made the impression, if "accu" or my nick "vaklaff", it doesn't matter much anyway. I let it go at first not to distract from the subject but now I think it would be better to make it clear before it sticks. I've also added it to my profile. As for "Vaklaff", it's is my nickname coming from the way how native English speakers usually pronounce my first name "Václav", it somehow grew on me :-)

Now back to the subject. Having processed all the information, I see three options for me:

1. External chargers. Duane kindly pointed to Mark's USB boxes (Classic, Spice)
2. Holders for disposable batteries like these two: Classic, Spice
3. Using a regulated power supply (like this one) clipped directly to the calculators contacts.
   

I'm leaning towards the third option, unless I am advised against it. In that case I'd probably prefer the holders and use disposable alkalines, unless that's a bad idea too :-) I see the external chargers as the least suitable option for me because of the regular need to rebuild the battery packs. But still it's an option if it turns out the other two are bad.

What do you think?

(*) For non-Europeans, we Czechs are the beer brewing Slavic nation wedged between Germany and Austria