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Full Version: hp-12c from HP.com arrives with dead batteries
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I did not feel like I should buy more of the hp-15C LEs so I decided to fulfill my long desire of owning a 12C. So I ordered an usual (not AE) model from hp.com and it has arrived today.
Only thing was it did not turn on out of the box. I replaced batteries and the machine is back to life.
I checked the cell voltage and they were 2.3 and 2.6 volts without any load.
Firmware date is 2008.6.28 and serial # is 4CY1150D5T.

I am not sure how long this was on the shelf, but I am wondering what is my odds of having received a unit with internal short.

The off state current is only a few microamps. That should take many years to discharge the 2032 cells if the calculator shut down properly. You might indeed have unit with a bad CPU or other components that allow for current leakage. However it could be just one bad cell. Since the cells are in parallel a single bad will will drain the other good cell.

Since you're able to measure the cell voltage, you likely have a DMM and that can likely measure current. Put the current meter in series with 3 volts powering the calculator. (2 AA batteries in a holder is easy to find if you don't have an external DC supply.) You should measure around 20ma when running a tight program loop, around .05 ma (IIRC) when on and idle and at most .005 ma when off.

Since the batteries are in parallel, do you simply connect the power supply with 3 vdc to any one of the two battery terminals for testing ?


Thank you very much for your advice. I measured these current levels and all fall in the range that you have identified. (except for the off current.. My RadioShack DMM can't detect micro amps) Maybe it was a bad cell. I feel much better now.