I'm assuming this means my battery is dead??

[john6206]

I have a gel battery on my 18' sailboat. It's a house battery (only battery) on a boat that has a pretty minimal electrical system. I think it's about 6 years old.

Battery should not have been dead - that is to say I'm pretty sure I didn't leave anything on. Battery charger didn't quite act the way it usually does - like it couldn't recognize the battery, and then it finally decided the battery is 97% charged, and it's a 6 volt battery (it's a 12).

Time for a battery funeral?

 

[kloudie1]

Prolly so. 6 years is pretty good life for use like that.

 

[dlochner]

Yep. It has led a full life.

When you buy a new battery, make certain the charger can charge the battery appropriately. Different types of batteries, flooded, AGM, gel charge at different voltages and currents. A mismatched charger is bad for battery longevity.

 

[john6206]

I may have asked for advice too soon. It seems to be charging now . . . . We'll see if it holds a charge.
I'll certainly test it before I go out on a trip.

According to the inter webs sometimes when it's deeply discharged, the smart charger can't recognize it.

Given that two people who know more than I do (when it comes to anything electrical - I'll just assume everyone knows more than I do) thought she was a goner - I'm not holding out too much hope, but we'll see.

Thanks -

John

 

[john6206]

After an hour on the charger it's telling me it's a 12 volt battery with 53% charge.
So I guess an hour ago saying it was a 6 volt battery with 97% charge was a good guess.

 

[Davidasailor26]

Get a digital volt meter and check its voltage after it finishes charging and you let it sit for a while. It should read above 12.7. The fact that the charger saw it as a 6V battery probably means it is dead and lost so much voltage just sitting that it was below the detection threshold for a 12V battery. That’s not a good sign.

 

[john6206]

That’s what I figured, but it’s worth a try.

 

[dlochner]

There are two battery characteristics that are at play here, one is the charged voltage and the other battery capacity. Over time all batteries lose the charge capacity, that is how many amp hours that can be stored. Age, charge/discharge cycles, and depth of discharge all cause a battery to lose capacity. A real killer is a very deep discharge, like the one you just experienced. Assuming you have a Group 24 battery, the battery has a storage capacity of about 75 amp hours when new and fully charged. The battery likely has much less than that now. There are ways to measure the remaining capacity, however they are time consuming and require some equipment. A rough estimate can be made by looking at how often the battery needs recharging, newer batteries can go longer before charging because they have more capacity than older batteries..

Voltage readings tell you what the state charge the battery is at relative to the batteries current capacity. A battery reading of 12.7 volts at rest, indicates the battery is at 100% SOC, but it does not say anything about the actual capacity of the battery.

It is near the end of the sailing season, so I wouldn't buy a new battery now, especially if you can eke out a few more amp hours from the current battery. Do a little research on batteries over the winter and stick a new one on the boat next spring.

 

[Benny17441]

If you can get it fully charged, connect your lights to it and see if they lasts a reasonable time before dimming. Batteries loose capacity to store power over their life but if discharged regularly deeper than 50% of charge or not charged fully after every use it will significantly shorten their useful life. Batteries left partially charged will sulfate the plates and diminish the capacity to store power. A battery may show to be fully charged at 12.7V but the capacity may be so diminished that it may only sustain a load for a very short time and with a rapid drop in voltage. Batteries on the average last 5 to 7 years.

 

[john6206]

Ok, so as the first two commenters said so eloquently, it’s done it’s job and served me well.

this morning, after 12+ hours on the charger, it’s only charged to 80%.

 

[Don S/V ILLusion]

Ok, so as the first two commenters said so eloquently, it’s done it’s job and served me well.

this morning, after 12+ hours on the charger, it’s only charged to 80%.

Depending on the charge rate, that doesn’t necessarily indicate much, however, if the charger is sufficiently sized, it sounds like you now have a large and heavy paper weight.

 

[Benny17441]

Ok, so as the first two commenters said so eloquently, it’s done it’s job and served me well.

this morning, after 12+ hours on the charger, it’s only charged to 80%.

Don't just get a replacement and stop there. Match the size of your deep cycle battery to your needs. Check that your charger is able to handle the type of battery you are getting. Some chargers can be adjusted to different types of batteries, others not. Gel batteries in general require that the charging voltage be limited to no higher than 14V. Some manufacturers suggest a lower limit for their Gel batteries, check the label. Make sure that you recharge the battery to 100% full after every use. Do not discharge any deeper than 50%. This lengthens the battery's useful life. You may know about residual voltage while charging or discharging, but just in case allow me to explain how it affects the battery's State of Charge monitoring. A battery is considered fully charged at 12.7V after resting for at least a couple of hours. A battery which just finished charging will show a higher voltage than its actual voltage, while a battery under load will show a lower voltage than its actual voltage. This makes it hard to determine instantly the state of charge of a battery in use. There are now battery monitors that will calculate the percentage of battery charge available but they are costly. A good enough approximation can be obtained with a regular volt meter for determining the discharge limits you may want to adhere to. When a battery is in use a voltage reading will indicate a lower voltage than the battery's actual voltage so it is safe to say that if your reading is 12.06V or higher that you have not exceeded the 50% capacity discharge threshold. Now a battery will continue to provide power beyond 50% charge but it is just at this point where the effects on the battery through repeated deep discharges will significantly shorten the battery's life. Sometimes depending on the circumstances we make a conscious decision to discharge beyond the 50% threshold but we try to avoid doing it too often.

 

[john6206]

@Benny17441
thanks for that.

when I read the book, “sailboat electrics simplified,” (or something like that). I remember thinking the section on batteries was not simplified nearly enough for me!

when I bought the gel battery (at Cabella’s) the guy, who Seemed knowledgeable, said I should probably throw away my 25 year old battery charger and buy the one they recommend for the gel batteries - I took him at his word.

I charged this one to 100%. by the next morning it had slotted in around 75%, and it’s been holding steady there for two days. I’m guessing that means I can get a weekend out of it.

like I said it’s a small boat and our electrical system is very minor. We usually have the fm radio and the vhf going while we are sailing. We likely won’t need the cabin lights, but the sun sets pretty early in northern Michigan in October, so hopefully we need running lights at some point.

In a typical sailing season I top off the battery in the spring and top it off again at the all-Star break. It’s usualky got plenty of life left when we pack it up in the fall. I fully charge it before I stick it in the basement for the winter.

 

[dlochner]

In a typical sailing season I top off the battery in the spring and top it off again at the all-Star break. It’s usualky got plenty of life left when we pack it up in the fall. I fully charge it before I stick it in the basement for the winter.

Gel and AGM batteries are very sensitive to being left in a partial state of charge. All lead acid batteries want to be fully charged. When a battery is left in a PSOC it ages more quickly. Charging your battery only twice a season will hasten its demise. Batteries also winter over better in the cold than in a warm basement so long as the battery is fully charged when left in the cold. In general chemical reactions slow down with cold, the electricity a battery produces is the result of a chemical reaction, so letting it be cold will slow the natural discharge rate.

Charge your next battery more frequently and don't worry about the winter cold.