From another posting, sailor Tom provided the link to a "State of Charge" chart. I didn't want to hijack the thread about a charger, but had another question about batteries. I have two five year old deep-cycle batteries that, fully charged, come up to 12.4V on a good day; the Guest charger I use over the winter sometimes only brings them back to 12.2V before shutting off. My question is whether the no-load voltage can also be interpreted from the chart as an indication that my batteries are only 60%-80% of what they used to be. They do not last as long as I once remember, but neither do I. So is the chart just illustrative, or does a battery that at best peaks at 12.2V telling me its only half the battery it used to be (and maybe shouldn't be trusted for another season)?
Battery Age
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charge or charger??
The low voltage is indicative of lowered capacity - approx 50%. howevr, all is not that simple. You didn't mention your charger voltage. If you are undercharging the batteries, that in itself could account for the lowered capacity and may be reversable. If you are not charging at around 14V, the batteries have sulfonated but a proper equalization will likely return lots of what was lost, If, however, the charger is operating properly, the batteries are on their way out. Don
The low voltage is indicative of lowered capacity - approx 50%. howevr, all is not that simple. You didn't mention your charger voltage. If you are undercharging the batteries, that in itself could account for the lowered capacity and may be reversable. If you are not charging at around 14V, the batteries have sulfonated but a proper equalization will likely return lots of what was lost, If, however, the charger is operating properly, the batteries are on their way out. Don
Charger puts out
about 13.5V, so I guess I would expect to see the 12.6V at the batteries. The voltages I'm stating are after a week of sitting; sounds like time for new batteries.
about 13.5V, so I guess I would expect to see the 12.6V at the batteries. The voltages I'm stating are after a week of sitting; sounds like time for new batteries.
You Did Good!
Batteries only last me about 4-5 years before I replace them. They may come back to a full reading, but won't hold as long as they get older. Just keep an eye on them, monthly, and fill the cells as they drop (distilled water only. Get it by the gallon at WalMart. Or out of your AC or dehumidifier). Believe it or not, I have had very good luck with Sam's Club Batteries. They are cheaper, also.
Batteries only last me about 4-5 years before I replace them. They may come back to a full reading, but won't hold as long as they get older. Just keep an eye on them, monthly, and fill the cells as they drop (distilled water only. Get it by the gallon at WalMart. Or out of your AC or dehumidifier). Believe it or not, I have had very good luck with Sam's Club Batteries. They are cheaper, also.
Battery charging
Flat charging voltage at 13.5 just won't do it. Recommend that you download and read the Ample Power Primer at www.amplepower.com to learn more about battery charging requirements. Stu
Flat charging voltage at 13.5 just won't do it. Recommend that you download and read the Ample Power Primer at www.amplepower.com to learn more about battery charging requirements. Stu
Don't replace 'em yet!
While I agree that the resting charged voltage should be much higher (12.7-12.8), before you go through the hassle and expense of new batteries you need to properly equalize them. If they're heavily sulfated (and they will be if you haven't done it before) then you may have to do it more than once. Check with the manfacturer's website for their recommended process or go to the Trojan website for a description of the process. If your Guest won't equalize then don't DREAM of installing new batteries until you get a high quality multi-stage charger that does. I have a Xantrax but there are others. Poor charging care probably sends more batteries to an early grave than anything else. Get an automotive hydrometer and check specific gravity of the individual cells. You should be at around 1.285 at full charge. This is the most accurate means of determining a battery's health. These readings are also how you monitor the equalization prcess. Basically it's just overcharging until the specific gravity readings are equal (as in equalization) at the 1.285 level. It burns off sulfated coatings on the plates in the process thereby returning the battery performance. If you don't have any cells with readings way out of whack compared to the others (shorted) your batteries may be candidates for a resurrection. It's worth a shot right? If you're going to live with wet cells you might as well learn about keeping them happy. If you'd rather not bother with all this then you'll want to consider going with gels or AGM's. You'll still need a good charger though. Hope this helps.
While I agree that the resting charged voltage should be much higher (12.7-12.8), before you go through the hassle and expense of new batteries you need to properly equalize them. If they're heavily sulfated (and they will be if you haven't done it before) then you may have to do it more than once. Check with the manfacturer's website for their recommended process or go to the Trojan website for a description of the process. If your Guest won't equalize then don't DREAM of installing new batteries until you get a high quality multi-stage charger that does. I have a Xantrax but there are others. Poor charging care probably sends more batteries to an early grave than anything else. Get an automotive hydrometer and check specific gravity of the individual cells. You should be at around 1.285 at full charge. This is the most accurate means of determining a battery's health. These readings are also how you monitor the equalization prcess. Basically it's just overcharging until the specific gravity readings are equal (as in equalization) at the 1.285 level. It burns off sulfated coatings on the plates in the process thereby returning the battery performance. If you don't have any cells with readings way out of whack compared to the others (shorted) your batteries may be candidates for a resurrection. It's worth a shot right? If you're going to live with wet cells you might as well learn about keeping them happy. If you'd rather not bother with all this then you'll want to consider going with gels or AGM's. You'll still need a good charger though. Hope this helps.
Not sure about Guest Chargers
I was minutes from buying a Guest charger, so I called and talked to Technical Services department at Guest about what charger to buy. She asked me one question, "Will you be using 12V power while dockside?" I told her yes, I might run some things, bilge blower or lights or the radio while on shore power with the charger energized. She told me that Guest does not sell a charger that will supply dockside loads. I was floored. Their chargers are only used to charge batteries after using the trolling motor all day for fishing.
I was minutes from buying a Guest charger, so I called and talked to Technical Services department at Guest about what charger to buy. She asked me one question, "Will you be using 12V power while dockside?" I told her yes, I might run some things, bilge blower or lights or the radio while on shore power with the charger energized. She told me that Guest does not sell a charger that will supply dockside loads. I was floored. Their chargers are only used to charge batteries after using the trolling motor all day for fishing.
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