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Discharge of resting battery?


KandJBm

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I have 2, 6-volt golf cart batteries that are 7 yrs old (used about 3 months each year). After charging them to full capacity (I think) and resting them for 12 hours, they come down from about 13.59 volts to about 12.75 volts. Then over the next few days they discharge about 0.1 volts each day while under no load. Has anyone measured their own golf carts to see how much they discharge under no load? 0.1 volts per day seems excessive to me. A sign of old age?

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Wet cells generally self discharge at a rate of 15% per month. They should be fully recharged every 60 days or so while not in use or put them on a "battery minder" type charger for "hands free" battery maintenance. If you are using a "battery minder" you still want to check water levels every 45 days or so (30 is preferable). If you are doing a periodic charge then water levels should be checked prior to recharging.

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12.73 is a good rested charge level but dropping a tenth daily has you down to 80% in a couple days and 50% in a week, not good.

 

On charge are you getting them up to the manufacturer's recommended charge voltage and holding them there to fully charge? That is usually 14.4 to 14.8 for flooded GCs.

 

 

If they are getting fully charged then it might be old age but before you give up on them take a specific gravity reading of each cell with a good quality tester and see if all the cells are close to the same reading. If you have a low cell a couple good cycles of equalization can do a lot to restore the battery.

 

If the cell has been weak for very long though that cell may have sulphated (due to the low charge level) and lost a lot of ability to hold a charge. A couple more equalize cycles may help restore the weak cell but likely it is going to remain a problem and you'll need new batteries.

 

Decent: http://smile.amazon.com/OTC-4619-Professional-Battery-Hydrometer/dp/B0050SFVHO

 

http://smile.amazon.com/Custom-Accessories-41119-Battery-Hydrometer/dp/B000HCX5JE

 

 

Not good: http://smile.amazon.com/Battery-Hydrometer-Professional-Disc-Type/dp/B0093U2B1Y

 

http://smile.amazon.com/FJC-46335-Battery-Hydrometer/dp/B008QF0BFK

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Wet cells generally self discharge at a rate of 15% per month. They should be fully recharged every 60 days or so while not in use or put them on a "battery minder" type charger for "hands free" battery maintenance. If you are using a "battery minder" you still want to check water levels every 45 days or so (30 is preferable). If you are doing a periodic charge then water levels should be checked prior to recharging.

I put a little bit more into the battery maintenance, as I have chosen to use this Battery Minder from Amazon with very good results. I kept the starting battery in our last motorhome for 8 years by using one of these every time that it sat for a week or longer.

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I put a little bit more into the battery maintenance, as I have chosen to use this Battery Minder from Amazon with very good results.

 

X2. It's a very sound investment. Just speaking in general terms.. most periodic campers 'generally' see 4-5 seasons out of their costco/sam's club type batteries. For a $50 investment.. it's not uncommon to get 8 or more so right out of the gate you've saved yourself money many times over by getting a 3 year extension on your initial layout. Not to mention that your battery capacities will be higher during their time in use.

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There can be 'ghost' loads on your batteries. Things like the memory on your radio, any led lights connected to electronics, your GPS battery charger if it is left connected, and many other possibilities. To find out if this is one of your problem, charge the batteries fully, really fully, and then disconnect the cables, Then check for voltage drops. If you still have them, it's time for new batteries. If the voltage drop is acceptable, you have loads on the batteries. Chuck

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The batteries were fully disconnected from the trailer after charging from the converter.

but I don't think they were fully charged to begin with.

I thought they came to rest at about 12.75 volts, but now I think they were still coming down from the 13+ when I disconnected them. It seems to take more like 24 hours of resting until they come off the charging voltage. Note that the batteries are not being used at this time and I have had them on the charger for about 3 days, but that still didn't get them fully charged. I am trying it all again after four days of further charging and no loads - fuses are pulled in the trailer! I ordered the battery minder and the hydrometer.

I think the converter will bring them to full charge even though it doesn't push the final amps in at 14.8v because it keeps pushing (floating?) at 13+ for four days now. Does that sound right?

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I think the converter will bring them to full charge even though it doesn't push the final amps in at 14.8v because it keeps pushing (floating?) at 13+ for four days now. Does that sound right?

The answer to that question depends upon what converter you have. Some of the cheaper converters have only one, constant output that is usually set for about 13.5V or so. But today there are converters that have multi-stage converter, it then might push up to 14+V.

 

The best way to get an accurate battery voltage is for it to sit in open circuit condition for several hours after charging and rest. A true resting voltage means open circuit, which most of us don't bother to do. You might find it helpful to take some time and read this article or some others of that type.

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The answer to that question depends upon what converter you have. Some of the cheaper converters have only one, constant output that is usually set for about 13.5V or so. But today there are converters that have multi-stage converter, it then might push up to 14+V.

 

The best way to get an accurate battery voltage is for it to sit in open circuit condition for several hours after charging and rest. A true resting voltage means open circuit, which most of us don't bother to do. You might find it helpful to take some time and read this article or some others of that type.

Read that article and already had read just about all of Handy Bob's blog and some other stuff too. But haven't found any simple statement that letting the converter run for some number of days without any amp draw will eventually fully charge the batteries. My converter is an Atwood 30amp that is for sale here: http://www.ebay.com/itm/ATWOOD-30-AMP-CONVERTER-W-CHARGER-RV-CARGO-TRAILER-/141384566574?hash=item20eb2d472e

I have not been able to find any charging details on it, even at the Atwood website, which does not list converters under its products(??)

Anyhow, just for information, the converter does seem to have fully charged the batteries after 4 days of charging them and measuring each cell with my new handy-dandy hydrometer. But I don't know the stages of charging it used during those 4 days.

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If it is not stated specifically that it is a multi stage charger, then it is not. The unit may completely charge the batteries after several days BUT it will continue to charge at a fixed rate and boil the battery dry eventually. As was stated this is to run 12 VDC lights etc. and then charge the battery, not a high quality charger.

good luck

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I take maybe a little different aproach when it comes to batteries as a whole. A start battery wheather it be a car or RV at 5 tears I look for weekness and at the first sign replace. For the house batteries I start looking at 6-7 years and again at the first sign of weekness replace(this gives me time to search as good a deal as I can find). With this in mind I never have battery failure or heart ache worry. And as to cost over a 5-7 year peroid, well whats my time worth from having a good time and a troublesome outing.

 

LEN

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Not having the specs for that Atwood unit and based on its price, my "best guess" would be its what I consider an older style (call it dumb) Converter/Charger and NOT a 3 or 4 stage so called "Smart Charger". The thing is iffffffffffffffff its more like a near constant voltage (around 13.4 to 13.6) source, it can to a degree "charge" a battery but not nearly so well or as complete as a "Smart Charger" which takes the batteries through progressive stages of charging beginning at say 14.2 to 14.4 volts (Trojan recommends an initial 14.8 volt charge) for Bulk and Absorption charging and eventually (once charged) reduce the charge rate down to a Float maintenance level at 13.2 or so volts and lower current. I would guess that if a smart charger were used, the battery life would exceed the same battery if it were charged all its life on a "dumb" or constant voltage converter/charger. SURE IT CAN "CHARGE" A BATTERY but I don't envision battery life expectancy to be near as good.

 

A so called 12 volt battery consists of 6 series cells each of around 2.1 volts (subject to temperature and state of charge) each so an at rest stabilized no load voltage of 12.6 to 12.7 is what I would expect. Having owned a ton of the old Converter/Chargers over the years, that 12.73 at rest voltage you mentioned is in line with my experience and expectation and I would expect near the same (at rest and stabilized) even if a so called smart charger were used, its just that as I mentioned its my opinion battery life would be extended by use of a smart progressive stage charger. HOWEVER it was also my experience if a constant voltage converter/charger is used for extended periods there is a possibility of overcharging and outgassing so keep an eye on water levels.

 

I have found instances of the self discharge rate increasing as a battery ages, perhaps due to sulfation and/or accumulation in the bottom of the cells and other natural chemical processes. I'm NOT a chemist

 

John T

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