Re: HP-35S : do the battery last that long? Message #5 Posted by Katie Wasserman on 8 Mar 2010, 9:24 p.m., in response to message #4 by Michael de Estrada
The 35S has a fairly high off-state current draw. I measured it on at around 10ua per cell. A typical CR2032 cell has a maximum rated capacity of around 220mah so you could expect about 2.5 years of battery life if you never use the calculator.
The amount of memory is insignificant to the off-state current draw for most calculators. What is stored in memory has zero effect on current draw in CMOS technology. What counts is:
1) circuit design -- cells in parallel with no blocking diodes is bad (the 12C+, 20b and 30b all have this problem).
2) silicon technology -- the leakage current on each gate. The Voyager series used chips that had near zero leakage current and the silver oxide button cells lasted for many, many years.
3) firmware design -- if the processor needs wake up often to scan the keyboard, update a RTC or do other maintenance functions, battery life is going to suffer.
-Katie
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