First Month with 50g

[Voldemar]

Last month I got my HP 50g Blue. Yesterday on my new calculator the low battery icon begun to display. Icon is strange. Looked at, only 40 days since I start to use the calculator. Today I replaced all batteries (4 AAA batteries and backup battery). Is it normal, batteries on HP 50g last only 40 days? I use HP 50g infrequently, while learn to operate. Much more I use my good old HP 35s. I have inserted SD card in calculator. Do SD card permanently in calculator drain batteries faster? Or it does not matter? And, is it necessary to change backup battery every time the low battery icon displaed, or backup battery lasts longer than main AAA batteries? Thank You for answers.