Dead batteries--advice?

[Oldrig]

To save money (hah!) this winter, I stored my boat in a storage lot, as opposed to a boatyard, intending to learn how to do almost everything myself.

The learning curve has already proven to be steeper (and more expensive) than I had hoped.

Last November, after running the engine (Yanmar 1GM) long enough to charge the batteries fully, before winterizing the diesel, I connected two inexpensive trickle chargers to the batteries, intending to plug the chargers in periodically. I left the batteries on the boat.

The batteries are sealed Exide Nautilus Gold Deep Cycle NG-24. They are about five years old.

When I closed up the boat, the batteries each measured 12.75 volts.

I only got to the boat a few times during the winter, and only plugged the chargers in for about 6 or 8 hours at a time (the owner of the storage lot did not want things plugged in overnight). While working on my boat this weekend, I noticed the red "dead battery" signal was glowing on one of the chargers. When I put my Radio Shack digital multimeter to the batteries, the charge registered 5.45v on one and 1.75v on the other.

These are disturbingly low--if not nonexistent--charge levels.

So, here's my question: Is there a chance that I can revive these batteries by pulling them from the boat, buying a good-quality "smart" charger and letting them charge slowly for a long time, or should I just bite the bullet and swing for a pair of new batteries?

When I posted this question on the Cape Dory board, one contributor who really knows marine electrical systems theorized that my Harbor Fright-brand chargers were bleeding the batteries. He suggested buying a high-quality charger and trying to save the batteries.

Any suggestions from electrical gurus on this board.

NOTE: These batteries are very heavy, and they're stored deep in a cockpit locker. The reason I left them onboard last winter was because my almost 64-year-old back is not in the greatest shape. Of course, now I'm going to have to remove these batteries in any case. If I act fast, I'm sure the owner of the lot, who is a friend, and the owners of nearby boats will be happy to pitch in. But they're all hard at work on their vessels, getting ready for launch dates in the next three weeks.

Thanks in advance for your recommendations.

And yes, I feel like a dunce. Several people warned me not to buy trickle chargers from Harbor Freight. I suspect that the chargers I bought were designed to remain plugged in for the entire time.

--Joe >:(

[Captain Smollett]

Those are incredibly low voltage readings.  Dead batteries generally still show over 10 volts.

Sometimes, when they are deeply discharged, you get a build-up of lead sulphate on the lead plates inside the battery.  If you blast them with a high current (say about 20 amps), you can sometimes "burn" off that coating, redissolve the sulphate in the acid and recover the batteries.

For a while.

I have done this...but it's never lasted.

Once a battery goes completely flat...and importantly SITS there for a period of time while flat...the plates themselves degrade.  You'll see very low capacities with those batteries, now...they won't deliver the amp-hours you are expecting.  Again, that's been my experience with trying to revive batteries that have gone flat and sat dead...you get SOMETHING, but it ain't much.

You might get some life back from them, but I would never as we say RELY on them for any length of time.  Hit 'em with a good charger and keep 'em topped up, and you might get some further use from them, but I would plan a battery purchase sometime in the not too distant future.

That's my take, anyway.

[CharlieJ]

Additionally- 5 yr old batts are edging in towards the " end of life span" time.

Get the charger anyway- that you can use in the future

[Oldrig]

Those are incredibly low voltage readings.  Dead batteries generally still show over 10 volts.

Sometimes, when they are deeply discharged, you get a build-up of lead sulphate on the lead plates inside the battery.  If you blast them with a high current (say about 20 amps), you can sometimes "burn" off that coating, redissolve the sulphate in the acid and recover the batteries.

For a while.

I have done this...but it's never lasted.

Once a battery goes completely flat...and importantly SITS there for a period of time while flat...the plates themselves degrade.  You'll see very low capacities with those batteries, now...they won't deliver the amp-hours you are expecting.  Again, that's been my experience with trying to revive batteries that have gone flat and sat dead...you get SOMETHING, but it ain't much.

You might get some life back from them, but I would never as we say RELY on them for any length of time.  Hit 'em with a good charger and keep 'em topped up, and you might get some further use from them, but I would plan a battery purchase sometime in the not too distant future.

Thanks John and Charlie.

Somebody on the CD board suggested that these readings were so low that my multimeter might not be working. I'm not sure how to check that out. However, I didn't realize how old the batteries were until I remembered that they were replaced after a winter storm surge flooded the battery-storage shack at my yard. That event took place in 2005--so the batteries are indeed 5 years old, going on 6 next December.

It's time to replace them.

Ugh!

--Joe

[s/v Faith]

You can check your meter using a couple of known reference points.

9v battery, check you car's voltage... etc.

  Unfortunately I doubt your meter is off... Probably new battery time (as has been mentioned).