I bought a HP-15C LE and a HP-12C 30th anniversary in 2013. Both have never displayed a low battery condition (and the display contrast hasn't decreased at all). Still both of them occasionally erase the RAM (at power-on) and show "Pr Error". Of course, I am going to change the batteries now. But I would like to know if it is normal that these devices don't show any kind of battery warning. My original HP-15C does show it.