There are usually two methods to detect the adequacy of the normal zinc manganese dry battery. The first method is by measuring the battery transient short-circuit current to estimate the battery internal resistance, and then judge the adequacy of battery power; the second method is with the ammeter in series a proper resistance value of the resistance. By measuring the battery discharge current calculated the internal resistance of the battery, so as to judge the adequacy of battery power.

The biggest advantage of the first approach is simple, with million with a table of the current file can be directly determine the dry battery power. The disadvantage is that the current test high, far more than dry battery to allow the discharge current limit value, in a certain extent affected dry battery service life. The advantages of the second methods is that the test current is small, the security is good, and the general will not have a bad effect on the service life of the dry battery, and the disadvantage is that it is very troublesome.

The author uses the MF47 type of the table to a new 2 dry cell and a section of the old 2 dry cell respectively with the above two methods to test the comparison. Assuming ro is dry battery internal resistance, RO is the internal resistance of ammeter, the second test method, RF is additional series resistance, resistance of 3 Omega, the power of 2W.

The test results are as follows. New No. 2 battery E=1.58V (with DC voltage of 2.5V voltage profile measurement), voltage meter resistance for a 50K, far greater than RO, so it can be approximately 1.58v is the electromotive force, or open circuit voltage. With the first method, the 5A multimeter direct current gear, RO=0.06 ohm internal resistance of the meter, the measured current is 3.3A. So ro+RO=1.58V / 3.3A = 0.48, ro=0.48-0.06=0.42. In the second method, the measured current is 0.395A, RF+ro+RO=1.58V 83019 0.395A=4 Omega, current 500mA file resistance to 0.6 Omega, so ro=4-3-0.6=0.4 ohm.

Old No. 2 battery measurement in the first method, first measured open circuit voltage E=1.2V, internal resistance of ammeter RO=6 of Omega readings for 6.5 Ma, multimeter 50mA DC current file, 184.6 Omega ro+RO=1.2V 83019 0.0065A PRG, ro=184.6-6=178.6 Omega. By second methods, the measured current is 6.3mA, ro+RO+RF=1.2V, 0.0063A=190.5, ro=190.5-6-3=181.5.

Obviously the results of the two test methods are basically the same. The tiny difference of the final result is caused by the reading error, the error of resistance RF, and the contact resistance. If the detected battery capacity is small, high voltage (such as 15V, 9V laminated battery), it should be adapted to increase the resistance of RF.