How long will a battery last? - Fiberglass RV


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Old 05-23-2016, 10:07 PM   #1
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How long will a battery last?

I'm planning on buying a group 27 battery and was wondering approximately how many days i can run lights and Tv on it if I use them all a few hours per night? I have 3 led lights, one is 12 Watts the other is 5 and there other is the Scamp porch light. The Tv is an insignia 19" 12v.
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Old 05-23-2016, 10:21 PM   #2
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Hi Rob. Your question can be answered by just adding up all the amp hour each item uses, and how long you will be using them. The incandescent porch light typically uses 10 times the amount of amps as compared to LED lights. Your TV should list the amps. Now remember that you never want to use more than 50% of your batteries capacity (if rated for 120 amp hrs, then never use more than 60 amp hrs). Good luck.
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Old 05-23-2016, 10:24 PM   #3
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Hi Rob. Your question can be answered by just adding up all the amp hour each item uses, and how long you will be using them. The incandescent porch light typically uses 10 times the amount of amps as compared to LED lights. Your TV should list the amps. Now remember that you never want to use more than 50% of your batteries capacity (if rated for 120 amp hrs, then never use more than 60 amp hrs). Good luck.
Dave & Paula
Thanks! I did change the porch light to an 1156 led bulb. I will try to find the amps the lights use, all I saw before is wattage so we'll see.
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Old 05-23-2016, 10:28 PM   #4
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We have a group 27 battery and run lights, television, water pump for showers etc. When traveling we have pretty much forgotten about trying to conserve the battery. We always have power.
That being said, we charge the battery from the tow vehicle when ever we are in motion and so seldom rely on the battery alone for more than two or three days .
If you want the most from your battery, refrain from running the fridge on 12V and be aware that the biggest battery hog is the furnace.
The use you describe is not much of a drain and could easily be supplemented by a flashlight and a good book if you misjudge!

I have stayed four days at the runoffs using all our 12V power as needed... including such things as incandescent lights, water pumps, DVD player, and television and digital converter and we stayed up late. We did charge the battery once for twenty minutes with jumper cables from our truck during that time.

We have since switched to all LED lighting and an LED backlit television.
Just one of the old incandescent bulbs uses more power than the new television.
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Old 05-23-2016, 11:07 PM   #5
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We have a group 27 battery and run lights, television, water pump for showers etc. When traveling we have pretty much forgotten about trying to conserve the battery. We always have power.
That being said, we charge the battery from the tow vehicle when ever we are in motion and so seldom rely on the battery alone for more than two or three days .
If you want the most from your battery, refrain from running the fridge on 12V and be aware that the biggest battery hog is the furnace.
The use you describe is not much of a drain and could easily be supplemented by a flashlight and a good book if you misjudge!

I have stayed four days at the runoffs using all our 12V power as needed... including such things as incandescent lights, water pumps, DVD player, and television and digital converter and we stayed up late. We did charge the battery once for twenty minutes with jumper cables from our truck during that time.

We have since switched to all LED lighting and an LED backlit television.
Just one of the old incandescent bulbs uses more power than the new television.
If it lasts for 2-3 days that would be perfect. Our fridge doesn't run on 12v nor do we have a furnace so we don't have to worry about those. Although we might add a 12 volt cooler in the future if we find we are camping at the parks non electric sites quite a bit.

Edit....I forgot to mention that I also have a shurflo water pump that will be used as needed.
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Old 05-24-2016, 05:09 AM   #6
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If you have the power in watts, divide by 12 (volts) to get the current (amps).

I = P/V

A 12 volt cooler will use a lot of power. A Coleman Extreme cooler is a better choice. I found a sterite box about the size of a shoe box at the dollar store that I make block ice. A milk jug filled with water also works
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Old 05-24-2016, 06:47 AM   #7
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Convert everything you expect to use while boondocking to 12v amps. If the unit gives you 120v amps, multiply it by 10 to get 12v amps. If it gives you watts, divide watts by 12.

Mulitply each item's 12v amps times the hours you expect it to get amp-hours it will consume each day.

Sum up all the amp-hours.

Find the amp-hour rating of your battery and divide by 2 (50%). A new group 27 is often around 95 amp-hours. The rating will degrade some as the battery ages. Half of 95 is 47.5. 50% is the recommended usage for a true deep cycle battery durability. (I'm not clear if the 50% rule of thumb applies to golf cart batteries.)


If your battery is only rated in cold cranking amps it usually means you don't have a true deep cycle battery.

Divide the useful battery rating by the sum of your amp-hours per day to get the number of days you can expect.

The accuracy depends on how close you estimate your usage.
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Old 05-24-2016, 08:55 AM   #8
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Bluetang99,

To add to what others have said, to determine the state of charge for a lead acid battery, you can use either a hydrometer or an multi-meter. The expected values for a 12 vdc battery that has rested for an hour or two (not charging or discharging) are:

100% charged: Ammeter will read 12.65 volts. Hydrometer will read 1.265 average specific gravity.
50% charged: Ammeter will read 12.24 volts. Hydrometer will read 1.190 average specific gravity.

For an AGM battery, a multi-meter must be used, and the values will be different.

-John

Edit: The state of charge values vary slightly by brand. Also, vary based on ambient temperature. For more details, check online.
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Old 05-24-2016, 09:19 AM   #9
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Estimating and Verifying Battery Usage

As others have said, battery consumption can be estimated fairly precisely if you can identify the amperage of each load and determine how long each load used.

I used a spreadsheet to identify the loads, amperages, and estimated duration of use. I then tested the battery usage by fully charging the battery, and then running the loads (lights, etc.) in the camper and recording voltage measurements taken each day over a period of 5 days. Edit: My goal was to determine whether my battery could be used for 5 days with a 50% remaining charge.
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Old 05-24-2016, 10:24 AM   #10
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I recently complete a study of batteries for RVs.

First read...the 12 volt side of life....google it to learn all you need to know about 12 volt deep cycle batteries....many batteries labeled RV/Marine deep cycle are not true deep cycle and will not stand repeated recharge cycles.
Reading this site will educate you about amp hours (AH).

After a lot of research I selected a AGM true deep cycle battery. The AGM (absorbed glass Matt) series of batteries last many years...require no maintenance and are sealed units and can be shipped via UPS or FedEx.
Amazon has the best selection and prices. When you search Amazon and read reviews of AGM deep cycle 12 volt batteries you will note most are sold to solar power applications but there are reviews by RV owners mixed in.
My final selection was...a universal battery group with 100 AH rating...group 27 size....Google AGM deep cycle battery...select Amazon to locate...Amazon lists this battery several,times....UB120001.
Cost was $149 plus $10 shipping via FedEx...quick delivery...arrived fully charged...it has preformed well in my 26 foot travel trailer.
This class of battery(AGM) is designed to last many more years than a standard liquid acid battery requiring maintenance and constantly adding distilled water.
Just install it and forget it.

I also ordered a compact voltage meter so I could monitor the condition of my AGM battery...(less than $10.)

Memo: be sure you have the space required for a group 27 sized battery before ordering.
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Old 05-24-2016, 10:46 AM   #11
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Originally Posted by Uplander View Post
....
First read...the 12 volt side of life....google it to learn all you need to know about 12 volt deep cycle batteries.......

After a lot of research I selected a AGM true deep cycle battery. ....
How interesting that you suggested the 12 Volt Side of Life articles, yet you choose a AGM battery... because in part one of the 12 Volt Side of Life article it says this:
Sealed gell and AGM batteries offer the convenience of no maintenance and produce less gas, so at first glance, they may appear more attractive than standard flooded cell batteries. There is a down side here, tho.... These batteries, especially the gell cell type, require precise control of the charging process to prevent permanent damage by overcharging. They also tend to be significantly more expensive and have a somewhat shorter lifespan. It all depends on what premium you put on the maintenance free aspect of it. In my opinion, the standard flooded cell battery offers better overall performance for the price and will probably last a lot longer in most common RV applications. The need to add water periodically is a small price to pay for the advantages you get.
I'm not saying you made the wrong choice at all (esp. if you have a proper charger for AGM). I only note that AGM might not be for everyone.

In fact I have been charging my battery just fine with a single 100 watt solar panel, and the controller is designed to work with AGMs also, so I might just go that route when the battery needs to be replaced. But if I were using the on-board converter (even with the Charge Wizard add on), I would stick with lead-acid.
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Old 05-24-2016, 10:56 AM   #12
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The charging of my AGM battery is managed by the multi stage converter in my travel trailer that is automatic. I either plug the trailer in at home or campsites or use my 3,100 watt Champion generator when boondocking...but always thru the RV's converter system.

Lead liquid acid batteries have a shorter life span than AGM batteries and will not tolerate as many recharge cycles as an AGM battery.
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Old 05-24-2016, 11:07 AM   #13
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Well since I replied somewhat off-topic I should address the OP's question directly.

If using only LED lights then 10 days would be no problem. The TV is the unknown, until you find out the amp draw. Even then, if you keep the screen as dim as you can tolerate, the amp draw will likely be notable less.

You also might have "phantom loads", that is things you don't think about but still draw small amounts of power, typically 24 hours a day. It can add up! I have a propane detector that draws 75 mA or close to 2 amp hours every day (1.8). I also think that the Charge Wizard on my converter draws a little even when off shore power. I know the LED blinks. Some fridge models also draw a little for the control board even if running on propane.

I have said it before, and here it is again... I really like having my TriMetric TM-2030 battery monitor. It tracks my battery usage and helps me budget my power usage to get the most out of the battery and keep it well maintained (not over discharged). You can get an idea by doing the math on the power draw of various things, and how long they are in use. But thats just an estimate. The TM-2030 is easier and more accurate. (About $200 if you DIY install however).

PS. Reading voltage is not a great way to measure battery charge, largely because you want to know the state of charge when you are using the battery (or have used it recently). Using a hydrometer is the best way (and no doubt even better than the TM-2030), but its a PIA and you always run the risk of spilling acid.
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Old 05-24-2016, 11:15 AM   #14
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Your question served me very well

Quote:
Originally Posted by Bluetang99 View Post
I'm planning on buying a group 27 battery and was wondering approximately how many days i can run lights and Tv on it if I use them all a few hours per night? I have 3 led lights, one is 12 Watts the other is 5 and there other is the Scamp porch light. The Tv is an insignia 19" 12v.
I'm so glad you posted this question, as all the answers have been so very helpful for me. I am now not quite so ignorant about the subject of batteries for my Scamp!
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