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can this battery be saved?

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cks
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126 Posts

Initially Posted - 07/06/2005 : 21:55:29

i have a 2 year-old deep cycle battery. my boat is moored. i left my vhf on all week and when i returned this weekend, of course, the battery was dead. my only way of keeping the battery cahrged is through the alternator on my outboard(1994 mercury 9.9). is it worth bringing the battery ashore and recharging it?

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 07/06/2005 : 23:43:22

A quality battery should last 10 years or more. (if properly maintained).
I'd think it's well worth bringing ashore to charge. (if it was my $70)

An extended period of time in a discharged state will ruin a battery... but I don't think a few days counts as an extended period. It should charge right up. Note that deep cycle batteries are usually slow charged. Most modern battery chargers will have a setting for them.

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 07/07/2005 : 01:34:18

It can't hurt to at least try to re-charge it. Keep a close eye on the electrolyte level and top off with Distilled water (buy at any grocery store). If you have a hydrometer calibrated for lead-acid batteries, you can assess the condition of the battery: After it has been on the charger for enough time to start freely bubbling hydrogen at 13.8~14.2 volts, it has absorbed as much charge as it's going to - at this point, test the specific gravity of the electrolyte in each cell, the S.G. should be close to the same in all six cells, about 1.25 if I remember correctly. You can also do a load/voltage/time test in your own garage (or in the boat) if you have a good VOM meter and a 12 volt device like a auto headlight bulb that has a known wattage. This involves charging the battery full, then placing a known load of about 10 amps on it (a typical auto headlight low beam is about 10 amps), and measuring the voltage and current flowing in the circuit repeatedly over a period of time with a good quality digital VOM that reads to 0.01 volts. For example, if the voltage at the start of the test is 12.2 volts, and the battery will power a 10 amp load for 8 hours while maintaining at least 12.0 volts, before the voltage starts to drop off below 11.7, you know that the battery has about 80 amp/hours of reserve capacity (typical for a size 24 battery, size 27's might go as high as 100 amp hours). If this agrees fairly well with the capacity stated on the manufacturer's label, the battery has at least some life left in it. On the other hand, if the label says the battery is supposed to deliver 80 amp hours, and in your test it expires after only 20 or 30 amp hours, then it's time to buy a new one. Flooded-cell deep cycle batteries also have a "service life" of a certain number of charge/discharge cycles. Every time the battery is cycled, the plates and the electrolyte deteriorate a little, and you have one less charge remaining on the "life" of that battery. The typical deep-cycle size 24 or 27 battery that you buy for $59 will maybe give 500 charge cycles of at least 75% of the rated capacity. From #500 to #800, the capacity will probably be deteriorated to maybe 50% of what it was when new, and after 800 cycles, the battery will likely die completely at any time, and not hold any useful amount of charge at all. This can vary with the quality of owner care and maintenance given the battery. You might get 1000 cycles out of it if you take really good care, or you might only get 50 if the battery is abused by excessive charging with the wrong kind of charger, exposure to very high or very low temperatures, leaving it in a discharged state for more than a few hours, or topping it off with tap water. Almsot all city tap water has some dissolved minerals in it, and of course chlorine and fluorine to kill disease microbes; lead-acid batteries should never be topped off with anything but distilled water (rain water captured in a clean container will do as long as it's not "acid rain" with a high sulfuric acid level).

Edited by - on

DanM
Captain

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USA
256 Posts

Response Posted - 07/07/2005 : 08:10:11

Wow! Thanks for the thorough disertation. Now you have me wondering about those trickle chargers you just leave attached to "top off". How do they affect the remaing life?
<font size="1">Every time the battery is cycled, the plates and the electrolyte deteriorate a little, and you have one less charge remaining on the "life" of that battery."</font id="size1">

Edited by - DanM on 07/07/2005 08:13:00

Leon Sisson
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USA
1893 Posts

Response Posted - 07/07/2005 : 09:24:44

DanM,<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Every time the battery is cycled, the plates and the electrolyte deteriorate a little, and you have one less charge remaining on the "life" of that battery."<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">I think this refers to a full charge cycle, from say 100% down to 50% (1.25 to 1.12) and back up. If the battery is only discharged a few percent before being recharged, I don't think that counts as one of its finite number of charge cycles.

-- Leon Sisson

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cks
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126 Posts

Response Posted - 07/07/2005 : 21:28:03

i'm getting the battery tomorrow. thanks everyone

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