The rechargeable battery info: 1900 mAH (1 battery)
A device that have input of 3V DC and output of 5 V / 500mA
If one rechargeable battery is inserted into the device,
I can expect that it can provide me (1900 mAH / 500 mA of 3.8 hours) of output. (or it can last me for 3.8 hours)
So, if two rechargeable batteries are inserted in parallel,
I can expect 3.8 hours * 2 = 7.6 hours of output
So, if the device only provide me 1 hour of output with 2 batteries inserted,
can I say that the circuit is faulty?
Suggestive that the device provide 3800 mA of output in 1 hour?
Also, a side note – the device becomes hot (temperature around 40 to 45 degree Celsius)
The 2 battery is insert into the following device:
Best Answer
First, stating the background based on the device now shown in the question:
The emergency charger shown is designed to provide 5 Volts at 500 mA, from 2 AA cells.
It is not clear from the device photo alone, and without specifications being provided, whether the device uses the batteries in series (will not work with a single cell inserted), or parallel as the question implies (will work even with a single cell inserted).
The circuit inside would be a boost converter, generating 5 Volts from a 1 to 3 Volt input. Typical boost converter efficiency is anywhere from 75 to 90 percent, depending on design and component selection.
Assumptions:
Assume roughly equal split of current draw...
So, even in optimistic conditions, the charger is expected to deliver less than 1 hour 14 minutes of power, from the above calculations. In reality, the current drawn would rise as voltage drops, thus causing faster depletion. Also, whichever cell has lower internal resistance due to manufacturing and life-cycle differences, would discharge first, loading the second into a quicker depletion.
Thus the observed 1 hour of operation is not unexpected.
Now, if the batteries were connected in series, as is possible, the following calculations change, the rest remain as above:
Thus, operation time would be about the same, but single battery operation would not be an option.
Additional notes: