How long will a battery last?

[Bluetang99]

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.

[David B.]

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

[Bluetang99]

Originally Posted by David B.

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.

[floyd]

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.

[Bluetang99]

Originally Posted by floyd

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.

[Raz]

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

[Steve L.]

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.

[John in Michigan]

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.

[John in Michigan]

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.

[Uplander]

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.

[gordon2]

Originally Posted by Uplander

....
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.

[Uplander]

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.

[gordon2]

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.

[Cybercuban]

Originally Posted by Bluetang99

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!

[Raz]

Originally Posted by gordon2

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.

We disagree here. These monitors were designed with large solar in mind. The smallest shunt is 100 amp. For folks using s single battery you are operating in the bottom 10% of the range. With a 1 millivolt per amp resolution accuracy at fractions of an amp, is doubtful. Unfortunately, when folks spend $200 on a battery monitor they wish to believe. Now folks that run an inverter, that's a different story. Still, spending $200 to get every ounce out of a $100 battery. There is a lot of snake oil on those solar sites.

After you charge with your panel a number of times you can get a pretty good idea how its going with a multimeter. Remember, they don't just read voltage. Raz

[Uplander]

New TVs (LED types) do not draw much power. I installed a 32" LED/HD Sony in my travel trailer...standard A/C powered. It only consumes 57 watts. I only watch it when plugged into campground electric or when my generator is running. I could run it off a simple 12volt inverter but television viewing is not that important to me. If you boondock a lot invest in a small inverter generator, they are quiet and will simplify your life. State campgrounds limit generator use to about two hours in AM and two hours in PM to keep the peace...most only permit quiet inverter type generators.

[gordon2]

Originally Posted by Raz

We disagree here. These monitors were designed with large solar in mind. The smallest shunt is 100 amp. For folks using s single battery you are operating in the bottom 10% of the range. With a 1 millivolt per amp resolution accuracy at fractions of an amp, is doubtful. Unfortunately, when folks spend $200 on a battery monitor they wish to believe. Now folks that run an inverter, that's a different story. Still, spending $200 to get every ounce out of a $100 battery. There is a lot of snake oil on those solar sites.
..

While I do respect your opinion (because it is apparent that your really know this stuff), I think there is more science behind the Bogart Engineering products than most so I would not lump them in with the solar snake oil crowd.

But you got me wondering so I just now ran a little experiment. I put a digital multi-meter in series with a LED bulb, powered by a 12 VDC outlet in the Scamp.

The digital meter read 102.5 mA with the LED on.
The TM-2030 readings showed an increase of .09 (90 mA) filtered* and .11 (110 mA) instantaneous with the LED on.

Perhaps this margin of error at very low levels will add up, but will also be less with things like a 1.5 – 3 amp draw from a fan. Bogart makes this claim: “With 100A/100mV shunt 0.00-300 Amps, resolution 0.01 Amp. ±1% ± least significant digit.”

But accuracy and cost effectiveness aside, the thing I really like about is the convenience. Just push a button a few times and get all sorts of readings. I don’t regret buying it at all. It would be a good test to compare the TM-2030 value of percent battery charge against a hydrometer reading, but since I like convenience and hate acid burns , I will leave that for another time.

Second would be the knowledge that its about impossible for me to unexpectedly end up with a dead battery, especially while boondocking in the middle of nowhere.

Maybe I like it so much because I paired it with the SC-2030 solar charger. Just one of the things I like is that in this config it tells you when there is spare solar power available, and you know that you can charge phones, etc. without even drawing from the battery (or at least drawing less because it is supplemented with solar).

Actually I do have a issue with my setup. I cannot for the life of me get a good spec sheet on the battery. I had to take a sawg at the capacity and more than any other variable, that one probably limits the accuracy for me. The next battery will be from a manufacturer who provided decent documentation.
-----------------
Methodology notes:

Everything in the camper was off except for a propane detector (rated at 75 mA but not measured) and the TM-2030 which uses about 30 mA when display is on (according the published specs).

The TM-2030 readings with the LED on were .21 and .20 (with the two values alternating but more often on .21). The filtered value was .20 (200 mA). With the LED off the reading was .10 but the filtered value was .11.

* Filtered values are an “average value” taken over 140 seconds and the figure used by the monitor to avoid monetary fluctuations in the data. For my measuring I allowed for five minutes with the LED both on and off before reading the filtered value.

[Raz]

There are lots of very clever people doing very clever things. I'm sure some work for Bogart. My point is that the single battery RV market is not their target audience. While to monitor the charging of a battery all you really need is a multimeter you seem to be having fun building a system and learning a lot. I'm sure you won't let me discourage you. When I was teaching I would set up 5 very expensive meters all measuring the same source. All would read slightly different. Electrical is the sloppiest of the engineering disciplines.

[Borden]

we got a deep cycle gel cell lasts a lot longer than old deep cycle batter was worth the extra cost, it has no holes can be mounted on side even no fumes

[gordon2]

Originally Posted by Raz

There are lots of very clever people doing very clever things. I'm sure some work for Bogart. My point is that the single battery RV market is not their target audience. While to monitor the charging of a battery all you really need is a multimeter you seem to be having fun building a system and learning a lot. I'm sure you won't let me discourage you. When I was teaching I would set up 5 very expensive meters all measuring the same source. All would read slightly different. Electrical is the sloppiest of the engineering disciplines.

I get all your points and have no arugment with them.

But about targeting...(or perhaps I should call it marketing instead of targeting by design)

... while the products might not be designed primarily for the RV market, they did add the suffix "RV" to one of the models because it has a different box, meant to be surface mounted in a.. you guessed it... RV