|Re: Low Battery Warning Sign After Replacement?|
Message #3 Posted by Rodger Rosenbaum on 1 Aug 2007, 11:07 a.m.,
in response to message #2 by PhysicsNerd
I posted some information on this subject:
As a Physics Nerd, you should have access to a digital voltmeter. Open up the back of your HP50G and touch the voltmeter probes to the ends of each cell to check its voltage. Do this with the calculator turned on. See if any one of the cells is substantially lower in voltage than the others. You may have a bad cell.
If you have access to a variable power supply as well, you can do the test I did. Connect the supply in place of the battery. Slowly adjust the supply from 4.5 volts to lower voltage. Make a note of the voltage when the low battery indicator comes on. Divide this number by 4 and that will be the per cell voltage that just causes the low battery indicator to come on. You can compare that number to the result I got.
As I mention in my post referenced above, on the HP50G that I have, the low battery indicator comes on when the NiMH cells are about 70% discharged. This has the obvious disadvantage that if you replace (and charge) them at that time, you will only be getting about 70% of the use per charge. But, it has the advantage that you have ample warning to replace (charge) them. This is good because normally NiMH and NiCAD cells have a very rapid drop in voltage when they are about dead, and you could only have a few minutes left when the low battery indicator comes on if it was set to come on when the cells were 99% discharged.
Have you been giving your HP50G expecially heavy use since you switched to rechargeable cells?
Edited: 1 Aug 2007, 11:11 a.m.