Healing Troubled Cells Richard Perez Here is what to do when the ole' battery is not storing what she used to. Many troubled batteries can have their capacity restored through healing procedures. These procedures vary from a series of overcharges to radical chemical surgery. First make sure that the patient is really sick In HP #28, page 36 I wrote an article about diagnosing battery problems. If you haven't read this article, then please do so before attempting to heal your battery. Chances are that your battery only needs to be fully recharged. The healing procedures in this article are only for sick cells. Performing these procedures on heathy cells will not improve their ability to store electric power. If your battery is already in good shape, then these procedures will only waste time, money, and materials. The procedures here are for sick cells, not dead cells. These procedures will not cure cells with internal short circuits, internal open circuits, or foreign material contamination. Lead-Acid Cells The biggest problem in lead-acid cells is sulfation due to chronic undercharging. Here the sulfate ions have entered into deep bonds with the lead on the cell's plates. The sulfate ions can bond with the lead at three successively deeper energy levels. Level One is the bond we use when we normally charge and discharge the cell. After a month or so at Level One, some of the bonds form Level Two bonds which require more electric power to break. After several months of being Level Two bond, the sulfate ions really cozy up to the lead and form Level Three bonds. Level Three bonds are not accessible electrically. No amount of recharging will break Level Three bonds. The longer the lead sulfate bond stays at a level the more likely it is to form a closer acquaintance and enter the next deeper level. This is why it is so important to fully, regularly, and completely, recharge lead-acid cells. INSERT ART Equalization Charges If the loss in capacity is due to Level Two bonding, then a repeated series of equalizing charges will break the Level Two bonds. Under equalization the Level Two bonds will first be transformed into Level One bonds, and then the sulfate ion can be kicked loose of the lead entirely and reenter the electrolyte solution. If your lead-acid cells have lost capacity, then a regime of equalizing charges is the first procedure to try. An equalization charge is a controlled overcharge of an already fully recharged cell. First recharge the cell and then continue to charge the cell at a C/20 rate for five to seven hours. During equalization charges, the cell voltage will become very high, about 2.7 VDC per cell. This overcharge contains the necessary power to break the Level Two bonds and force them to Level One. Once they reach Level One, the bond is easily broken and the sulfate ions reenter into solution in the electrolyte. EDTA Treatment If a bond spends several months at Level Two, it eventually enters the depths of Level Three. The Level Three bonds must be chemically stripped from the plates. This is a job for an organic acid called EDTA, a close chemical cousin of vinegar. EDTA stands for the compound "ETHYLENEDIAMINE TETRAACETIC" Acid. In chemical techie terms, EDTA is a "chelating agent.". EDTA comes in several forms. Use the tetraacetic variety. The EDTA procedure is simple. Use one tablespoon of the EDTA powder for each quart of electrolyte in the cell. Mix the EDTA with a small amount (an ounce or two) of distilled water and add it to the cell. Recharge the cell and give it an equalizing charge. Recharging the cell speeds up the reaction and allows the EDTA to strip the Level Three bonds from the surface of the cell's plates. After this reaction takes place, the dead Level Three materials fall to the bottom of the cell as a precipitate. The reaction can take from several days to several weeks depending on temperature, recharge rate, and depth of Level Three bonding. Once the Level Three bonds are stripped from the plates, new lead is exposed and can enter into Level One bonding with the sulfuric acid electrolyte. The amount of EDTA used here is a ballpark guess. If your cells are badly riddled with Level Three bonds, then you may wish to repeat the EDTA treatment in a month or so. Feedback from hundreds of HP readers who have tried EDTA indicates that it will not harm the cell. For a complete discussion of EDTA treatment see HP #20- pg. 36, and HP #21- pg. 36. Alkaline Cells Most alkaline cells with diminished capacity suffer from electrolyte carbonation. This phenomena usually occurs after 15 to 20 years in nicad and nickel-iron cells. The potassium hydroxide (KOH) electrolyte enters into chemical combination with atmospheric carbon dioxide (CO2) and forms potassium carbonate (K2CO3). This removes the KOH ions from the electrolyte and makes the cell less able to conduct electricity. The decrease in electrolyte conductivity makes the cell reach a lower voltage much more quickly under discharge. As such, electrolyte carbonation appears to the cell's user as diminished capacity. In pocket-plate nicads, electrolyte carbonation is usually caused by not maintaining a sufficiently deep layer of mineral oil floating on top of the electrolyte. The mineral oil layer protects the electrolyte's surface from contact with the atmospheric CO2. One-eighth of an inch of mineral oil is all it takes. If alkaline cells are charged hard (>C/20) when they are full, the cells will gas violently. This gassing agitates the oil layer and works air (which contains about 0.03% CO2) into the electrolyte. Testing for electrolyte carbonate level is possible via titration. For the specific procedure see HP #15, page 23. It is more expensive to test a cell's carbonate concentration than it is to replace the electrolyte in a cell. So the test procedure is usually skipped if the cell is over ten years old. Electrolyte Replacement To cure carbonation just replace the electrolyte. The best procedure is to buy an electrolyte replacement kit from a nicad dealer. This kit comes with return privileges for the old carbonated electrolyte. It is very important to dispose of the old electrolyte safely because it contains a small amount of cadmium Ð a toxic material. The procedure is simple enough, but use caution. KOH can burn exposed skin and eyes. So look sharp! Wear rubber gloves, long sleeves, and tight fitting goggles. Gently shake the cell to stir up any sediment. Slowly empty the cell by inverting it over a plastic bucket or washtub. Refill the cell with new electrolyte, and add an 1/8th inch layer of pure mineral oil. Refill the now empty container with the old electrolyte and proceed to the next cell. After all cells are done, ship the old electrolyte back to the nicad dealer for proper disposal. If you are daring and want to mix your own electrolyte, see HP#15, page 23 for technical details. I don't recommend doing this because this method offers no easy avenue for the old electrolyte's disposal. Also the small amount of lithium hydroxide used in the electrolyte is difficult to obtain and potentially dangerous in its pure state. Buy your replenishment kit from a dealer who will give you the standard mix. The replacement electrolyte usually has a specific gravity of 1.25 and contains 10 grams of lithium hydroxide per liter (40 grams per liter if the cells are nickel-iron). No Sure Cure If you run the appropriate procedures on your cells, then you should notice an increase in capacity. If you don't, then something else is wrong. The procedures here are specific cures for specific problems. Your cells may have other, possibly terminal, problems such as contamination. I recall hundreds of beautiful, virtually new, Edison nicads that were terminally contaminated with diesel fuel. I've seen lead-acids ruined with dirty hydrometers. Your cells are a chemical machine. Keep their insides pure and they will return your efforts with long life. Access Author: Richard Perez, c/o Home Power, POB 130, Hornbrook, CA 96044 ¥ 916-475-3179 EDTA Bryant Labs, Peter Barnett, 1101 5th St., Berkeley, CA 94710 ¥ 415-526- 3141. Cost: $22.50/500 grams. Trailhead Supply, 325 East 1165 North, Orem, UT 84057 ¥ 801-225-3931. Cost: EDTA, $10/LB. ppd. Alkaline Replacement Electrolyte UtilityFree, POB 228, Basalt, CO 81621 ¥ 800-766-5550 A four gallon electrolyte refill kit costs $59. plus shipping. It includes gloves, funnel, return labels, and instructions. You can ship the spent electrolyte back to UtilityFree (prepay shipping) and for a $20 fee they will properly dispose of it.