# At what voltage is a deep cycle battery empty?



## budgetprepp-n

Hey guys I'm doing some experimenting seeing how long I can run some different stuff using my 12 volt deep cycle
battery. I know if I let the voltage get too low it can damage the battery but what's the cut off point?
How many volts? ----


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## Leon

if it's up at around 12 its full, if its down to like 5. Past that it can wear the battery out.


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## rickkyw1720pf

A better way then using a volt meter is to get a hydrometer .
A hydrometer is an instrument used to check the concentration of acid in a battery by measuring the density of the fluid. The higher the concentration of battery acid, the higher the specific gravity. Also use a hydrometer to measure the state of charge of a car battery or deep-cycle batteries in a solar-power system. Check batteries regularly with a hydrometer, as opposed to a voltmeter, to ensure accurate readings.


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## budgetprepp-n

Leon said:


> if it's up at around 12 its full, if its down to like 5. Past that it can wear the battery out.


I'm in trouble then,, Are you sure? The meter on my battery is usually around 14.5 after charging for a few hours on a sunny day
and I don't think I have ever seen it go below like 12.9. I hope I'm not running overcharged. 
When I was putting this solar system together That's something that we never really addressed was what battery voltage should be. 
I just sort of turned it on when it was done and it's worked good so far. (keeps the lights on every night)
I have really not had to mess with it or repair anything
--The small solar system that I have was sort of designed and engineered by members of this forum as it was built---- 
I must confess I'm still learning about solar stuff


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## rickkyw1720pf

Don't worry about over charging unless you are boiling the water away. Once the battery is fully charged any other current is just going into heat. 14.5 sounds about right when charging a battery. A 12 volt battery should not be discharged below 11 volts (with out a load). Remember also if the specific gravity gets to low the battery can freeze. Also if a battery gets to low most chargers will not charge them because of the high internal resistance, any current from the charger will look like a fully charged battery. Even a simple cheap battery hydrometer from Walmart will tell you more about the state of your battery then a volt meter. The voltage on the battery will very do to the different loads and after a load is removed it will take awhile for the battery voltage to reach its top static position.


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## Leon

budgetprepp-n said:


> I'm in trouble then,, Are you sure? The meter on my battery is usually around 14.5 after charging for a few hours on a sunny day
> and I don't think I have ever seen it go below like 12.9. I hope I'm not running overcharged.
> When I was putting this solar system together That's something that we never really addressed was what battery voltage should be.
> I just sort of turned it on when it was done and it's worked good so far. (keeps the lights on every night)
> I have really not had to mess with it or repair anything
> --The small solar system that I have was sort of designed and engineered by members of this forum as it was built----
> I must confess I'm still learning about solar stuff


Oh no I'm wrong then, what type and brand name is the battery? Yeah, usually when I CHARGE my batteries they go like 13-14 but just sitting there at full charge they throw 12.3-12.4 during operation. I have ran them down to 5 before and that's when the unit cuts out. Specifically I am talking about my 1800 watt solar generator by Duracell / solutions from science. I think it has a bank of 3 or 4 deep cycles on it. Mine are funky though they're pretty new and it must be stored at full charge and it has it's own metering and controller in the case. It's heavy as all hell, there might even be five in there so I'm thinking it's the whole bank reading not just one. Are you talking about a single battery?


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## Leon

rickkyw1720pf said:


> Don't worry about over charging unless you are boiling the water away. Once the battery is fully charged any other current is just going into heat. 14.5 sounds about right when charging a battery. A 12 volt battery should not be discharged below 11 volts (with out a load). Remember also if the specific gravity gets to low the battery can freeze. Also if a battery gets to low most chargers will not charge them because of the high internal resistance, any current from the charger will look like a fully charged battery. Even a simple cheap battery hydrometer from Walmart will tell you more about the state of your battery then a volt meter. The voltage on the battery will very do to the different loads and after a load is removed it will take awhile for the battery voltage to reach its top static position.


Yeah mine are all sealed deep cycle batteries, you guys using marine deep cycles?


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## budgetprepp-n

Leon said:


> Yeah mine are all sealed deep cycle batteries, you guys using marine deep cycles?


 Yes I'm using a deep cycle "12 volt 114 [email protected]" I have more than 1 tied together but the voltage reading is the same on just one battery or all of them at the same time. They are wired + to + I forget if that's series or parallel

For now I'm using just one battery and I'm using an inverter and seeing how many hours I can run different types of 110 volt bulbs from
a fully charged battery (about 14.3 volts) until it gets down to about 12.5 I also check the true watts on each bulb with a KILL-A-WATT meter. Then I also have been doing the same on different types of 12 volt bulbs and comparing them.

That's why I was asking when a 12 volt battery needs to be shutdown to prevent damage to it. 
I would like to push the battery right to it's limits to get a true reading on how many hours one battery can run a certain type of bulb 
It's easy to do a 15 minute test and then estimate how long a bulb would run.
But I want to make sure before I change anything in the solar system I have now. So far the results have not been what I expected At all. I may be making some changes and running some 110 volt bulbs for lighting instead of the 12 volt ones.

But if I do before I make any changes I'll do a post on my results and get some input and ideas on how to go about it. 
This forum is a great spot to "pick brains" and gather information.


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## Leon

well if you're getting like 11 at low reading you're not doing a dang thing to that battery. Sounds like you are well within reasonable boundaries.


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## PaulS

Any lead acid battery will produce 12 volts when it is tested without a load when it is dead. The only way to know when your battery is dead is with your standard load on it. 

If your average load is 5 amps then test the voltage with a 5 amp draw. If the voltage under load drops below 9 volts then it has been 80% discharged and needs to be charged. If you consistently discharge to that level and then immediately recharge it, then your battery should last 7 to 10 years. If you normally discharge beyond that point your battery will last half as long. If you leave it in a discharged state for more than 12 hours you will begin to lose capacity and your 114 amp hour battery becomes a 100 amp hour battery. 

Hard sulfate forms on the battery cells when it is discharges and is left in a discharged state. There is no way to return hard sulfate back to its soft state. You should never discharge a lead acid battery (that includes "gel cell" batteries) more than 80%. To test your car battery, you place a load on it with the starter (requires that the coils be grounded to prevent ignition) for 10 seconds and if the voltage drops below 9.5 volts the battery is either no good or needs to be charged. All capacity tests with a lead acid battery requires a full and equalizing charge. (an equalizing charge uses a higher voltage than the typical charge at the last stages of the charge for a period of several hours) The equalizing charge completely charges all the cells (equalizing the plate conditions) to the maximum capacity for the battery.

In usage a battery needs an equalizing charge at least every month in a deep cycle application. Use distilled water to prevent the buildup of metallic salts that will eventually short the cells. If you have run the battery down to the point where it shows 5 volts you have already damaged the battery and I would expect it to fail within four years of life. Batteries do not store energy - they make it from a chemical reaction and that reaction works the center of each plate first. As the center of the plate transfers the chemical change that active section of the plate spreads out to the rest of the plate. If the plate center stays in a discharged state for a prolonged period then it will begin to erode and lose its material to solution that eventually falls to the bottom of the case. The difference between a deep cycle battery and the one in your car is the amount of room under the plates for this material to collect. Both types of battery can have the same amp/hour capacity but the deep cycle battery will have an inch or more space between the bottom of the plates and the bottom of the case. The number and size of the plates in each cell determine the amp/hour capacity and the the number of cells determine the voltage. 

Ok, lesson is over for now but keep in mind that you have to check the battery voltage under load and when the voltage, under load, drops below 9 volts your batter should be recharged.


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## HuntingHawk

I think the important part is the low voltage shut off of the load on the battery.


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## exmilitary

I do let any of my batteries drain below 10.5 volts. Anything below will cause the places to sulfate.
There are devices that claim they can remove sulfate off the plates by pulses of DC voltages, but I have to try one and see if they work.


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## budgetprepp-n

HuntingHawk said:


> I think the important part is the low voltage shut off of the load on the battery.


 Ok you definitely have my attention. Please explain about this shut off. 
They make something that will shut down the battery draw if it gets too low?


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## Montana Rancher

My understanding is don't draw your batteries down below 50%. You can do it about 100 times but each draw down lowers the batteries viability.

If you keep them 50% and above you will find the max life.


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## paraquack

My personal experience seems to go along with what most are saying. My motorhome uses 2-6 volt deep cycle golf cart batteries in series to give me 12 volts. Using a cigarette lighter socket volt meter, I monitor my batteries when I dry camp (no power available). I try to never go below 12.0 volts. A long time ago a tech for a battery company told me 11.88 volts was the point where serious damage would start. My batteries are about 14 years old and are still capable of supplying enough power to run my lights, fridge, water pump, and the inverter for TV (for about 2 hours at most per day) for the entire weekend. Another thread ha raise interest in switching to LED "light bulbs". Obviously proper watering with distilled water and twice a year cleaning of the cables/posts and the top of the battery to prevent power leakage to ground probably helps. There are battery monitors out there that have the capability to operate a shut down relay exist, but at around $300, I'll pass.


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## Fallon

The desulfitization gizmos that send a pulse to the batteries at a given frequency sound like snake oil, but aren't. They have some sound science behind them & validated rigorous testing with positive results from many parties. Sulfitization isn't always the problem, so they aren't a magic bullet.

Mans chargers have a desulfitization setting on them, or you can get a quality dedicated device for under $20 or so when I looked a while back.


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## srtayl

OK, so, here goes.

Every Battery has a Life Cycle, Duty Cycle, and Plate Degradation Specification. The following link will answer quite a few, if not all, questions about batteries and how to manage/maintain them safely with longetivity.

Interstate Batteries FAQ

As for charging, you 'cannot overcharge a battery so long as you are supplying the 13.6 VDC (12-15 volts) and no more. What happens if you do not have a sensing circuit (like what auto battery chargers have built into them) your system can supply current (amperage) at to high of a level which will, as alreadt mentioned, be removed from the battery in the form of heat (and Hydrogen gasses) as the acid boils and oxidizes (for lack of the proper term) the batteries lead plates ruining the battery. Remember, HEAT KILLS... just about everything electrical/electronic, so look into a way to shut off, or sense your batteries charge and the charging systems controls.

Battery capacity is measured in Amp-Hours and not voltage... that being said, it is difficult to determine your batteries capacities at any time in it's service life without testing them with a gravometer (load tester), but the following link has a 'guess-t-mate' way of predicting the health of the battery and expected run-times.

A hydrometer tests the acid's specific gravity and thereby provides an indication of the acids dillution/contamination... it does not indicate the health of the lead in the battery, that has to be done with a load tester as state above.

Hope all this helps.


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## paraquack

Here's a link with a good tutorial.
http://www.batteriesinaflash.com/deep-cycle-battery-faq


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## paraquack

Here's a link with a good tutorial.
http://www.batteriesinaflash.com/deep-cycle-battery-faq


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