HP-42S Scientific Calculator current consumption
Some people complains about fast battery drain when using this calculator.
this should not happen, as the current consumption is very low under normal circumstances.
Assuming that the calculator passes the full self-tests, this suggests one of two possible causes:
1) - The battery batch you are using presents very high internal resistance due to a manufacturing defect or maybe they are out of date.
This results in a very fast voltage drop at the battery terminals especially under load (with the machine in power on state).
2) - Your calculator current consumption is way above the average.
This one is easy to spot as long as your multi-meter is able to measure current.
Here are the normal current consumption on a HP-42S, brand new, barely used:
(Test done using an external 4.5VDC power source. Any 4.5VDC 3R12battery will do,or else you may use 3 x 1.5VDC AA or AAA batteries in series installed in a battery holder)
Power off state: 9μA average (9 micro Ampere, to be clear)
Power On idle: 0.3mA average
Power On pressing keys: 2.5mA average
If you machine have much higher values, specially when in powered off state, then you need to check possible current drainage causes, starting from previous battery leakage (most common cause IMHO) to a bad bypass capacitor.