All Things Being Equal (Batteries)

As we’re cruising on the East Coast and occasionally reading the New York Times, we feel it behooves us to be politically correct. We are already at a disadvantage in this regard due to the fact we have no burgee halyards to either masthead, and so cannot fly our owner’s signal or yacht club pennant correctly. The situation is made worse by the fact that in the land of Hinkleys we have neither varnish on deck, overhangs fore and aft, nor polished blue topsides.

We woke up this morning pondering this problem when Linda had an epiphany. “We’ll equalize the batteries! It’s been three months, they are overdue, and there are bound to be one or two cells lower than the rest, which has to be depressing for the poor dears.”

So, we’ve been sitting in this lovely anchorage in Somes Sound, with the smells of the verdant forest wafting around us on deck, and the smells of batteries being equalized wafting below. We started the process this morning at 0900, and should be done by 1300.

All seriousness aside, folks, if you have lead acid batteries of the flooded cell type (i.e. you can add water), if you want them to last they should be equalized every two to three months. Equalization helps get rid of any lead sulfate stuck to the plates which normal charging doesn’t put back into solution. If the batteries do not get equalized, the lead sulfate gradually hardens and then it will never come off, and you’ve lost capacity and life-a truly depressing situation.

With a 12-volt system equalization takes place at between 15 and 16 volts. With a 24-volt system, equalize between 31 and 32 volts. Five hours usually does it-and time period starts when the batteries are otherwise fully charged.

If you have any DC equipment which is voltage sensitive, halogen bulbs for example, leave this gear off until you’ve finished. Hydrocaps have to be removed as well as they’ll overheat from all the gassing. (For an article on hydrocaps, click here.)

Keep the hatches open and air the boat well. You will be giving off lots of hydrogen gas – which is highly explosive (as in the Hindenberg dirigible!). However, it is lighter than air and will rise and leave the boat, as long as you’ve got good ventilation.

How do you know when equalization is complete? The only way is with a hydrometer, which measures the specific gravity of the batteries’ electrolyte. For most batteries a specific gravity of around 1285 equals a fully charged battery. However, what you are looking for is the weakest or lowest cell.

Right now, as this is being typed, our 24V bank has all the cells reading 1280 to 1285 (uncorrected for temperature) and one cell reading 1265. That’s the laggard, and it is the one we’re watching. When it gets to 1280/1285 we know we’re finished with equalizing. It is also the cell that gets periodically checked to know the state of the battery (you always measure from the lowest cell).

If you are new to hydrometers and checking batteries, you will want to take care with splashing. The electrolyte is a solution of sulfuric acid. It stings, will burn holes in clothes, and obviously you want to wear glasses of some sort to protect your eyes.

The specific gravity is a function of battery temperature. If the batteries are cool, like ours are, due to the water temperature in Maine (54 degrees in this anchorage – yuck) you correct the hydrometer reading down. If the batteries are warm, the SG gets corrected up.

(There’s a lot more detail on this subject in Offshore Cruising Encyclopedia, including the temperature correction graphs).

We’re surrounded by a group of kayakers (who look somewhat chilly). But they are all smiling. The fact that we’re taking care of the weakest member of our (battery) society is no doubt making itself felt. It makes us feel good too, knowing that our batteries will have a long, healthy, and productive life…

Posted by Steve Dashew  (August 10, 2001)

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