I’ve heard about this for years and always assumed that since the chemistry was not designed for recharging, any claim that this could be done was just so much hot air.
A few months ago such a claim was made here on SolidSignal. This made me consider this yet again and so I designed a few tests.
The first test would have to include a recharging method, a cool-down period, a low current test, and a higher current test.
The recharging method was using a constant current power supply I built many years ago to recharge NiCd batteries. It was designed to be able to deliver up to 300 mA at 9 Volts. This charger is capable of charging one AA alkaline battery at a constant low current for these tests. The advice in the most recent article suggested a very low charging current. My charger could get down to 26.1 mA and so that was the current used.
The test was started with a “dead” AA Kirkland alkaline battery reading 1.239 Volts. (Voltages were measured with my Beckman 3010 multi-meter.) The initial charge was using a constant current of 26.1 mA for 29 hours 8 minutes. Multiplying current * time, we get a total of about 760 mAHrs put into the battery. If this battery was a 2 AHr battery, then that’s not even half the charge of a new battery. My judgment was based on reaching 1.60 Volts. Another test, based on total AHrs put into the battery, might be a better way to test.
In any case, once the battery reached ~ 1.64 Volts while charging and ~ 1.61 V resting, the charging portion of the test was concluded.
The battery was allowed to rest until there was no significant loss of voltage over a 24-hour period. This took about 28 days, from 08/16 to 09/13, and the voltage was now 1.450 Volts.
On 10/11/2014, another 28 days later, the resting battery was reading 1.44 Volts (The third decimal value was found not to be needed for these measurements.)
I used a Joule Thief circuit to test the battery voltage with minimal drain – somewhere around 10 mA – and then attached a 5 Ohm 1 Watt resistor for five seconds. I measured the voltage with just the Joule Thief circuit (JT), then added the resistor (JT+R) . The voltage after five seconds of running the JT+R circuit was then recorded. The resistor was shown to add an additional 200mA of drain to the JT circuit, for a total (JT+R) of 210 mA.
The Recharged battery started at:
1.42 Volts (JT), 1.05 Volts (JT+R), and 0.99 Volts (JT+R+5sec)
I found a similar AA Kirkland alkaline battery, partially used, at 1.48 Volts resting:
1.48 Volts (JT), 1.41 Volts (JT+R), and 1.40 Volts (JT+R+5sec)
The second charging test was to charge for a set amount of time, but when I started doing that, I noticed the battery got up to 1.88 Volts in about another 24 hours and then, at about 36 hours, it was lower at 1.79 volts. I decided to stop the charging at that point. I let the battery rest for 16 hours and then tested it.
The Recharged battery started at:
1.568 Volts JT+5sec) and 1.125 Volts for (JT+R+5sec)
The AA Kirkland alkaline battery, partially used, at 1.48 Volts resting:
1.484 Volts (JT+5sec) and 1.397 Volts (JT+R+5sec)
Comments and Conclusion:
I found that my general-purpose charging circuit was using one Watt, for about a total of 60 hours to charge the battery, twice, with some very minor tests between to show the battery was not yet fully charged. This means the circuit used 0.56A * 60Hrs or ~ 33.6AHrs to charge a 5 AHr battery. This means that somewhere around 33 AHrs was used in hopes of being able to charge a battery to supply about 5 AHrs at best. Also, 60 hours was used to accomplish this task.
In my opinion, the time, effort, and energy used to charge a standard alkaline battery is not worth the return. The 60 hours of charging did not return the battery to anything close to its original capacity. It wasn’t even close to a similar battery that was partially discharged at about 1.48 Volts.
I assumed one Watt to charge a battery to 1.8 Volts, thus getting ~ 0.56A. The one Watt was measured with my Kill-O-Watt meter, so it could have been anywhere between 0.6 – 1.4 Watts. It was supplying 26.1 mA to the battery when it was 1.4 to 1.88 volts. I selected 1.8 volts to use in the calculation, so that was where the 0.56A came from. P = I*V or I = P/V for 1/1.8 = 0.55555, so I rounded to 0.56 A (560 mA) to supply 0.026A (26 mA) to charge the battery. The charging circuit is using more than 19 times the current than the amount of current used to charge the battery. I’m sure a more efficient charging circuit could be built, but after these tests I’m equally sure of two things: (1) Charging a standard alkaline battery is going to be far more wasteful than charging a battery chemistry designed for recharging, and (2) no amount of reasonable charging of a standard alkaline battery will ever be able to come close to matching a new alkaline battery.