The RV house battery can be one of the most perplexing things to figure out when you are trying to figure out how your motorhome or travel trailer works. It sounds simple. You have, say, a 100 amp hour battery. 100 amp hours, wow! That should last for days, right? Wrong! It really isn’t rocket science, but it is math, when it comes to figuring out how long that 100 amp hour battery will actually last in the real world.

Difference Between Amps and Amp Hours

First off, we need to understand the difference between Amps and Amp Hours. The basic breakdown between amps and amp-hours is that amps are a unit of electrical current, while amp hours are the units of “current storage capacity.”

How to Calculate Work Hours on a Battery

The first thing we want to do is convert to watt hours. Most devices you use will have their watt usage listed on them. You can convert Amp Hours to Watt Hours using the formula below:

Amp Hours X Voltage = Watt Hours

If we add in our example 100 Amp Hour battery size we get: 100AH X 12v = 1200 WH

That means that our 100 amp battery can sustain about 1200 watts from devices for an hour or 600 watts worth of devices for two hours.

In a real-world example, our humidifier lists a wattage of 280w on low and 470w on high. That means that a single 100 amp hour battery can power it on the low setting for 4.29 hours and for 2.6 hours on high.

It would be great if devices told us specifically how many amps are used, then you could simply divide the battery capacity by total device amps. But most devices give you a rating in Watts, which is why we need the above formula.

How many Amp Hours do you really get from a 100ah battery? 

The above formula, however, exists in a theoretical bubble. Like most things in life, calculating how long a battery will actually last isn’t quite as simple as knowing the formula. There are several factors at play that reduce that theoretical Discharge Time into real-world usage.

Low voltage cut off

Most batteries can be damaged if they are depleted below a certain level. So there is a low voltage cut off point that you don’t want to deplete your batteries beyond. You may have a device that automatically makes the battery unavailable at the low voltage cut off point or you may have to monitor your battery manually.

Battery Type

The type of battery you use in your RV also makes a difference in how many usable amp-hours you actually have. Lead-acid batteries are less forgiving than lithium batteries in how far they can be depleted, so you have less available amp-hours, despite the battery’s amp hour rating.

A lead-acid battery isn’t recommended to be drained below 50 percent capacity. That means your 100 amp hour battery in real-world applications will actually only last around 40-50 amp-hours.

A LiFePO4 (lithium iron phosphate) battery can be safely discharged to “0” percent capacity. You wouldn’t normally discharge it that low, but you can expect about twice as many usable amp-hours as you would get from a lead-acid battery.

Excessive Parasitic Draw Rate

There are numerous appliances and devices that, even when not in active use, have control boards or other elements that draw 12V power from your house battery. This is called a parasitic draw.

It is normal, but can significantly affect how many amp hours your battery will last between charges. And don’t forget about the little lights in your storage bays, booster antennas, and other devices that are easy to forget about that can draw down the battery. It all adds up!

Getting Less Than A Full Charge

If you don’t fully charge your battery, it’s not going to provide all the amp hours that you expect. A 100 amp hour (or whatever capacity is specified) battery will come much closer to maximum efficiency if you keep your batteries topped off with a full charge.

Calculating Your Watt Hours

There is no simple way to calculate the watt-hours you’ll use on a daily basis without a battery monitoring device. To do so, you need to know how many watts per hour each of your devices use and then multiply that times how many hours per day you use that device. Then you add all of the individual totals to get an estimate of how many watt-hours you need.

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Why You Never Get all the Power Capacity From a Battery

There are several reasons why you will never get all the power capacity from a battery that it is rated for.

Batteries don’t discharge evenly

You don’t use the exact same devices in exactly the same manner for exactly the same amount of time day in and day out. This means that your battery is discharged at a different rate depending upon how heavy the load is that you are putting on it.

The heavier the load put upon the battery, the less capacity it has, meaning it will be depleted sooner than you might hope.

Batteries are rated for 5 amps over 20 hours of time

A battery’s amp hour rating is based on a consistent load of 5 amps. What that means is that a 100 amp hour battery that has a constant load of 5 amps on it should last 20 hours.

That is all well and good if you were always going to be pulling a consistent draw of 5 amps from the battery, but that’s not how the real world works. In some instances, you will be drawing less than 5 amps per hour and sometimes more, which means the actual amount of time your battery will last is going to vary from day to day. 

Chargers may not fully charge

Your battery may not always get a full charge. As mentioned earlier, batteries degrade over time and usage, so as the battery gets older, it will not be charged fully to 100 amp hours, no matter what you do.

There are also different types of chargers. A multi-stage charger has a more efficient way of charging; thus, keeps your battery’s ability to achieve a near 100-percent full charge for a long time. A single-stage charger is much more blunt. It simply doesn’t have the finesse of a multi-stage charger and can sometimes shorten the life of your battery.

Cycle Life of a Battery Count

Whether your battery is lead acid or lithium it has a finite number of cycles that it can be depleted and recharged. This is the cycle life of the battery. Generally, lead-acid batteries if maintained properly can be good for a few hundred cycles. Lithium batteries on the other hand can last thousands of cycles. 

But the number of times and how deeply a battery has been depleted and then recharged affects how much capacity it can hold. The more times it has been cycled, the less able it is to hold its maximum capacity.

So how long does a 100 amp hour battery last?

As you can see, there is no one-size-fits-all answer to this question, because there is no one-size-fits-all way that we each use our RV battery on a day to day basis.

But hopefully, this helps you understand how the battery works and just what that 100 amp hour rating means in the real world. If you can understand that and how to determine the number of amps your various devices use, it’ll go a long way towards making your life easier on the road.

You’ve probably heard all of the perks of using a sealed deep cycle battery for your power scooter, solar array or battery backup system. One of the biggest reasons that these batteries have grown in popularity is that they require very little maintenance to have a long life. Nevertheless, even the tiniest bit of maintenance could extend your battery life significantly and save you money in the long run. Let’s look at a few ways that you can add months (and maybe even years) to the life of your battery.

Full Cycle Charging Vs Opportunity Charging

One of the easiest ways to extend your battery’s life is simply by making sure that you are giving your battery a chance to fully charge in a complete cycle each day. This allows your battery to go through a conditioning phase which prevents sulfaction damage to the plates. Opportunity charging is when you plug your battery in sporadically throughout the day, and then unplug it as you need it, without ever completing a full cycle. This does not give your battery the time needed to condition itself properly, and will ultimately deteriorate your battery life.

Understanding Depth Of Discharge

Another thing you can do to protect your battery is to learn about the depth of discharge specifications of your battery. Most deep cycle batteries are built to handle a 50% depth of discharge, but some can handle up to 80% discharge. If you are always recharging your battery in a complete cycle, you could expect to get just over 220 complete cycles when you drain the battery 80% each day, whereas you would get almost 750 complete cycles if you only discharge 50%. On the other hand, you also don’t want to constantly charge your battery when it has been discharged less than 10%. Like opportunity charging mentioned above, this will prevent your battery from ever completing a full cycle, and will cause damage.

Proper Storage

When not in use, your deep cycle battery should always be fully charged. These batteries are designed with longevity in mind, and they do not tend to lose a lot of charge when sitting idle. Thus, charging them fully before you place them in storage, and then checking them periodically to top them off if they discharge to 20% DoD will allow you to keep them in good shape without having to constantly keep a charger plugged in. While we’re talking about storage, temperature is another key factor. Batteries stored in freezing temperatures or extreme heat will break down faster than other batteries. It is always best to bring your deep cycle batteries inside and store them in a cool dry place to prevent damage.

Slow Charging

Finally, the best way to extend your battery life is by making sure to charge your battery as slowly as possible. For instance, slow charging overnight is much kinder to your battery’s internal components than using a rapid charger for only a few hours. This is because rapid charging increases the internal temperature of the battery.

With these four quick tips, you can give your battery the lifespan it deserves. Most deep cycle batteries can last up to six years with proper care and charging (depending on the frequency of use). It’s up to you to make sure that your battery isn’t being damaged by your charging routine.

When connecting multiple solar panels in a 12-48 volt off-grid system, you have a few options: parallel, series, or a combination of the two. In this article, we’ll give you the basics on wiring solar panels in parallel and in series.Let’s start off with a quick comparison of parallel circuits and series circuits.

Parallel circuits have multiple paths for the current to move along. If an item in the circuit is broken, current will continue to move along the other paths, while ignoring the broken one. This type of circuit is used for most household electrical wiring. For example: when you turn off your TV, it doesn’t also turn off your lights.

When wiring solar panels in parallel, the amperage (current) is additive, but the voltage remains the same. eg. If you had 4 solar panels in parallel and each was rated at 12 volts and 5 amps, the entire array would be 12 volts and 20 amps.

Series circuits have only one path for current to travel along. Therefore, all the current in the circuit must flow through all the loads. A series circuit is a continuous, closed loop – breaking the circuit at any point stops the entire series from operating. An example of a series circuit is a string of old Christmas lights – if one bulb breaks, the whole string turns off.

When wiring solar panels in a series, the voltage is additive, but the amperage remains the same. eg. If you had 4 solar panels in a series and each was rated at 12 volts and 5 amps, the entire array would be 48 volts and 5 amps.

Remember: just like batteries, solar panels have a negative terminal ( – ) and a positive terminal ( + ). Current flows from the negative terminal through a load (current consumed by a piece of equipment) to the positive terminal.

Wiring Solar Panels in a Series Circuit

• Connect the positive terminal of the first solar panel to the negative terminal of the next one.
• eg. If you had 4 solar panels in a series and each was rated at 12 volts and 5 amps, the entire array would be 48 volts at 5 amps.

Wiring Solar Panels in a Parallel Circuit

• Connect all the positive terminals of all the solar panels together, and all the negative terminals of all the panels together.
• eg. If you had 4 solar panels in parallel and each was rated at 12 volts and 5 amps, the entire array would be 12 volts at 20 amps.