Hello,
Just an update on this topic. Thanks to the advice from members of the forum, I finally bought some AAA Panasonic Eneloop Pro batteries (900 mAh). What a difference they make: With the set of Philips 1000 mAh, I had to recharge every week with light every day use but with the Eneloops and a more heavy use of the calculator, I am already on my second week without any need to recharge (not even the low battery warning showing). It is a pity that I could not find them anywhere locally, so eBay it was.
Thanks and regards,
Miguel