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A digital voltmeter is the only way to accurately monitor the voltage level of the batteries. Analog voltage meters can't easily show you the difference between batteries with a 50% charge and batteries with a 30% charge. This particular voltage meter came from Camping World and plugs into a standard lighter socket. |
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You can extend your battery's life by keeping your battery charged properly and avoid deep discharges. A charge "cycle" is considered to be a discharge of the battery from 100% to some point not lower than 20%, and then charged back up to 100%. Running your batteries down totally flat will have a very negative effect on the lifespan of them. This chart is designed to be used when monitoring a battery under load. This chart is a little more useful to the average Pop-Up'er, as we are most interested in monitoring the state of charge of our battery bank while it is actually in use. |
The above "Chart" copied from "The 12volt Side of Life (part 1)" |
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I printed out the above chart, covered it with plastic, and mounted it with Velcro just under the digital volt meter. Having the chart next to the volt meter gives me a way to directly compare voltage readings to percentage equivalents on the chart. Also note the "red", "yellow", and "green" LED lights on the meter. The corresponding LED lights up in relation to battery health, loosely matching up to the colors on the chart below it. |
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| At this point, it's also important to note that the battery voltage will be affected by temperature.... The chart above, and most other ratings applied to Lead/Acid batteries assume that the battery is at room temperature: 21 degrees C or about 70 degrees F. As the temperature of the battery drops, so will the fully-charged voltage reading. I have found a lot of conflicting information about this phenomenon, but it seems to be safe to say that for each 10 degrees F drop in temp, you can expect to see the voltage drop about a tenth of a volt. (.10 volt) That means that a battery at 32 degrees F with a no-load voltage reading of 12.35 volts is fully charged. | |||
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The above "Quote" copied from "The 12volt Side of Life (part 1)" |
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| Battery capacity (how many amp-hours it can hold) is reduced as temperature goes down, and increased as temperature goes up. This is why your car battery dies on a cold winter morning, even though it worked fine the previous afternoon. At freezing, the battery's capacity is reduced by 20%. At approximately -22 degrees F (-27 C), battery AH capacity drops to 50%. Capacity is increased at higher temperatures - at 122 degrees F, battery capacity would be about 12% higher. Even though battery capacity at high temperatures is higher, battery life is shortened. Battery capacity is reduced by 50% at -22 degrees F - but battery LIFE increases by about 60%. Battery life is reduced at higher temperatures - for every 15 degrees F over 77, battery life is cut in half. In reality, this is fascinating information, but isn't really terribly important. Most RVers experience a wide range of temperatures and conditions, so your batteries will average out just fine... I only include this information to give you some feel for the fact that temperature plays a part in battery life and capacity. Don't worry about it! | |||
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The above "Quote" copied from "The 12volt Side of Life (part 1)" |
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I currently use 2 ea. (T-125) 6 volt "Trojan" batteries each with a Reserve Capacity minutes@ 25 Amps of 235. I have found that with day temps in the 70's and night temps in the low 60's; my batteries still retain ~60 to 70% the initial charge. (mild western Washington climate)Supplies for this mod. cost ~$14.00. The chart I just copied and printed it out on my home computer/printer. Plastic to cover the chart I picked up at work for nada. |
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"Dry camping" comes with a very real need to keep track of the
charge level of your batteries. This mod. is a simple and cheap way to accurately
monitor your batteries at a glance with confidence.