Q & A — December 2004
By Capt. Ken Kreisler
2: Extending battery life
I use a pair of deep-cycle,
12-volt house batteries and have heard of a charging process known as
equalizing that can extend battery life. Can you explain? A.L.,
During equalizing the charging voltage is boosted to as high as 15 or 16 volts. However, if the current (amperage) is not controlled—that is, held to no more than five percent of the battery’s amp-hour rating—the internal temperature of the battery can exceed 125ºF, and therefore the battery may “cook.” For example, a battery with a 200 amp-hour rating should be equalized with 10 amps of current. Sealed or gelcell batteries cannot be equalized, as the sealed case prevents distilled water from being added or gas pressure equalized. The more sophisticated and, therefore, more expensive battery chargers and inverters with multistage chargers equalize deep-cycle batteries automatically.
If your charger does not have this feature, you’ll want to equalize one battery at a time. First, to prevent damage, shut off all D.C. electronic equipment that cannot tolerate such high voltage. Whenever you work around batteries, you should wear protective eyewear, gloves, and clothing. And do not leave the batteries unattended.
To begin the process, fully charge the battery at an ambient temperature of no more than 80ºF. Check each cell to make sure the electrolyte is at the proper level. Leave the vented caps on. As you apply the current, several things will happen. During any battery charging—and especially with this process because of the high voltage used—gas will be emitted. Since this is an explosive mixture of hydrogen and oxygen gas, proper ventilation is crucial, and avoid any open flame or spark.
The vigorous action caused by the elevated voltage will loosen the crystallized sulfate left on the plate, causing it to fall to the bottom of the battery casing and exposing fresh lead to the electrolyte. If any cells begin to “spit” or emit liquid, terminate the equalizing cycle.
Take specific gravity readings every 15 minutes with a hydrometer until all the cells read 1.26. One or two of the cells may be a little slow in reaching this level, and if after several hours of testing, a cell reads lower than the rest by 0.05 or more, it may be dead. Once the weakest cell reaches full charge, the process is over.
Next, top off the electrolyte level with distilled water. Let the batteries rest for at least one hour before measuring the voltage and the specific gravity of the cells again. Use the measurements you get at this reading as the baseline or “full charge” mark for that particular battery. It’s also a good idea to log specific gravity readings once every three or four months to track trouble within the cells.
Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: firstname.lastname@example.org. No phone calls, please. Or visit the Maintenance forum at powerandmotoryacht.zeroforum.com.
This article originally appeared in the November 2004 issue of Power & Motoryacht magazine.