Join Date: Apr 2006
Location: Spokane, WA
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I have completed the experiment as far as I am inclined to at the moment. I thought that you would like the results. I will be unavailable for the next week and a half, not sailing, but my daughters wedding. I will respond to any questions on my return, or just let this thread die it there is nothing further. I hope this has been useful to some.
Both batteries were fully charged over several days (< 0.1 amp draw @float voltage) and left dormant, open circuit without charge or load, for 48 hours. The open cell voltage was then recorded. The negative terminals connected together using an 8 AWG cable. The positive terminals where connected together using a Fluke 8060A 5 ˝ digit (three decimal places, at the 12 V range. It will measure 1/1000 of a volt) DMM in current mode measuring in the 2A to 1 milliamp range between both positive terminals. I recorded the current every 15 seconds for the first hour and a half and then at increasing intervals. The temperature of the batteries was also recorded.
Battery #1 had an open circuit voltage of 12.628V and battery #2 an open circuit voltage of 12.681V before the start of the test. At time zero, at initial connection the current between the batteries was 30.35 mA (I had stated before that the current was 300 mA and I apologize, I was reporting from memory, never a good idea) [1 mA = 0.001 Amps] The scale on the DMM was reduced to 200 mA.
The results are shown in the attached graph. Additional observations are that there was a current reversal where the temperature and other fluctuations within the batteries caused changes in the open cell voltage. The current measured at this point was less then 1 mA and stayed less then 1 mA. (Just a quick calculation, IF the 1mA drain was into a resistive load and NOT into the capacitive load of the battery, i.e. the 1 mA was lost and not recovered, that current drain would represent a battery life in excess of 15 years with no recharging [discounting self discharge]. What this means is that this drain is less then the self discharge rate). The battery temperature remained stable at between 77 deg F and 80 deg F, fluctuating with the ambient temperature. The final voltage of the batteries at the end of the test were battery #1 = 12.629V and battery #2 = 12.681V. Battery #1 is the one at 90% capacity and battery #2 the one at 55% capacity. Yes, the open cell voltage for the bad battery was higher then the good battery.
There are two types of fools...
One says this is old, and therefore good..
The other says this is new, and therefore better...