I have always wondered how long a 12V Battery will last on an inverter. It always seems like a guessing game, and no one has the answer. Sure, there are graphs and theoretical durations on the amp hours and voltage of the battery. Which, you have to try to calculate and figure out if what you are doing applies to the graph.
Since we couldn’t find a realistic test of common batteries with common power consumption, RVgoer decided to test the 3 most common 12V batteries. We have set up a 1000w inverter and tested an AGM battery, a deep cycle flooded battery, and a car battery.
This post will go in-depth on the full testing of these 3 batteries. We will review how long each battery has lasted as well as the performance of the inverter, including:
- Testing Setup
- 12V Battery
- AGM Battery
- Deep Cycle Battery
- Car Battery
Results: How long will a 12V battery last with an inverter?
Before we deep dive into each battery and how long they lasted, here is a quick snapshot of the overall results:
As suspected, a brand new AGM battery was the longest lasting 12 volt battery when it came to capacity for an inverter. An AGM battery can last 164 minutes with a constant 800 watt load. Read more below on why 800 watts was the best choice for testing.
The runner-up battery was a typical RV acid-flooded deep cycle battery lasting 96 minutes with the same 800 watt load. Finally, as suspected, the poorest performing battery was a car battery designed for bursts of power to start a car and does not provide high-capacity long-term power. The car battery lasted only 58 minutes with the same inverter load.
Table of Contents
- Results: How long will a 12V battery last with an inverter?
- Testing Setup
- AGM Battery
- Deep Cycle Battery
- Car Battery
- Final Thoughts
Testing Setup
As with any scientific experiment, let’s review the setup, parameters, and how data was collected. First, let’s determine our goal, which is to determine the battery life of an inverter.
Next is the “why.” Why does it matter to know how long an inverter will last? No one wants to get stuck without power, especially if they have no idea how long it will last. An inverter provides ac power, allowing you to power any appliance or an electric device. But how long will that inverter give you ac power before there is a full discharge and you need to connect to a battery charger? Good question and this post will disclose the full data depending on your 12V battery type and capacity.
Power Inverter
The inverter that was used for this experiment was a 1000w inverter. This particular one is a Powermax 1000 Watt power inverter that is a pure sine wave. A pure sine wave mimics the actual sine wave of AC current. It works for all electrical equipment, including sensitive electronic devices such as tablets and smartphones.
Why did we use a 1000w inverter when we know you can get a 5000 watt inverter? The reason is that a 1000w inverter is the universal size for inverters. They are portable enough for your car, RV, or boat. Yet provide enough power to run a large fan, fridge, and several lights. Also, a 1000w power inverter is a great size to use as a solar inverter for solar power. Plus, when you talk about a 5000 watt inverter, that would involve a very large battery bank with many 200ah batteries connected in parallel to keep the power going.
Capacity
You can’t talk about battery power unless you know what you are trying to power. An inverter battery will last longer the less power it is trying to provide. So how do we answer how long the battery will last when it depends on the load? This experiment considered the most common type and power consumption needed.
We took a 6 amp motor (720 watts), which could be anything from a fridge, a coffee maker, or a crockpot. Then, we also determined that you may want a smaller load, such as lights. So we added 72 watts of lights. This could be 6 LED lights in your RV or boat.
This gives us a total load on an inverter battery of 792 watts. I like round numbers, so let’s say this is 800 watts of continuous power being asked of these batteries.
12 volt battery
Now let’s dive into the batteries and how they were tested. There are many types of 12v batteries on the market. You have your old-school flooded batteries, which are very economical and have worked for many years. You also have newer types of batteries coming into the market, including gel and lithium-ion batteries.
In this experiment, we have focused on the 3 most common types of batteries used for inverters. These are AGM batteries, Deep Cycle batteries, and Car Batteries.
In each battery type test, we connected batteries to the inverter and a multimeter. The inverter provided the AC voltage, and the multimeter constantly checked the DC battery voltage. The 800 watt appliances and lights were connected to the inverter receptacle.
Testing
Testing was done by first recording the at-rest voltage of the battery. Then power the inverter and measure the battery voltage at 10 minutes intervals and the AC power output. At each 10-minute interval, the battery voltage was recorded, and ac power was checked. The battery was discharged when the appliance and the lights turned off due to no more ac power. The battery voltage was recorded at this point, and the readings were placed on a graph.
AGM Battery
The AGM Battery tested is brand new with a battery storage of 80 amp hour capacity. This type of battery is a deep cycle battery, but instead of being flooded with acid, there is an absorbent glass mat that makes them more spillproof and absorbs shock better.
An AGM battery is also known to hold a charge better and last longer than regular deep-cycle batteries. They are also the preferred solar battery when used with solar panels. Knowing this, we started our first test expecting this battery to provide the longest-lasting battery life. The starting at rest voltage was 12.9 volts. Here are the results:
| 10 minutes | 12.18 volts |
| 20 minutes | 12.17 volts |
| 30 minutes | 12.15 volts |
| 40 minutes | 12.10 volts |
| 50 minutes | 12.06 volts |
| 60 minutes | 11.99 volts |
| 70 minutes | 11.93 volts |
| 80 minutes | 11.87 volts |
| 90 minutes | 11.81 volts |
| 100 minutes | 11.73 volts |
| 110 minutes | 11.66 volts |
| 120 minutes | 11.55 volts |
| 130 minutes | 11.45 volts |
| 140 minutes | 11.33 volts |
| 150 minutes | 11.17 volts |
| 160 minutes | 10.95 volts |
| 164 minutes | battery discharged |
| appliance and lights turn off | at-rest voltage 11.30 volts |
The final result is that an AGM battery rated at 80 amp hr, will provide 164 minutes of continuous AC power for 800 watts.
Here are few notes that we found interesting when testing this.
AC Voltage
We noticed that even though the battery voltage dropped, the inverter kept providing consistent power that ranged from 114 volts to 116 volts. So even just before the battery was fully discharged, the inverter provided consistent full power. There was no reduction in power to the lights or appliances. They ran at full speed and then just shut down. No reduced power was noticed.
Another interesting fact is that the inverter fan turned on more often as the voltage dropped. The inverter worked harder to make the 116 volts ac power with the lower battery voltage. And the temp of the inverter remained constant from 86 to 88 degrees Fahrenheit.
Voltage Drop
Another observation is the rate of the voltage drop as time went on. When the battery was above 12 volts, the voltage drop stayed around 2 to 4 volts per ten minutes. As the battery capacity depleted, the voltage drop increased to as much as 20 volts per ten-minute interval.
Deep Cycle Battery
The next battery test for capacity was an acid-flooded deep-cycle battery. This type of battery has been around for a very long time. They are the most common type of RV battery and boat battery. They hold a charge well and can drain down or deep cycle without much harm.
They are a lead-acid battery and typically don’t perform as well as AGM batteries. As we test this out, let’s see if that still holds.
The specific battery tested is a 65 amp hr battery that came with my RV. It is 3 years old and was maintained on the RV or a battery charger. The starting voltage at rest was 12.74 volts. Let’s see how it did:
| 10 minutes | 11.57 volts |
| 20 minutes | 11.56 volts |
| 30 minutes | 11.51 volts |
| 40 minutes | 11.44 volts |
| 50 minutes | 11.37 volts |
| 60 minutes | 11.20 volts |
| 70 minutes | 11.06 volts |
| 80 minutes | 10.96 volts |
| 90 minutes | 10.62 volts |
| 96 minutes | 10.19 volts |
| appliance and lights turn off | at rest voltage 11.56 volts |
The final result is that the deep cycle battery has less capacity than an AGM battery. Although the AGM battery has 20% more capacity in amp hours, it lasted 70% longer than the flooded deep cycle battery.
Also, the same behavior in voltage drop and temperate applies to the deep cycle battery as to the AGM battery.
Car Battery
The third battery tested was a regular starting car battery. Why did we test a car battery when a deep-cycle battery likely holds the most capacity? The reason is that many people use an inverter connected to their car or truck, and we want to see how it can perform with these batteries.
For this battery, we tested an AGM car starting battery that was 5 years old. Even though it is an AGM, a car battery is only designed to give bursts of energy to get the starter moving. That is what they referenced as cold-cranking amps. Also, being 5 years old, the capacity is depleted. But since most of us have a car battery that has a few years in it, we wanted to test the expectation of using an inverter on your car or truck.
Well, the results are in, and as suspected, the car battery was the poorest performing of the bunch. Take a look below. The starting-at-rest voltage was 12.3 volts
| 10 minutes | 11.43 volts |
| 20 minutes | 11.34 volts |
| 30 minutes | 11.23 volts |
| 40 minutes | 11.09 volts |
| 50 minutes | 10.88 volts |
| 58 minutes | 10.60 volts |
| appliance and lights turn off | at rest voltage 11.36 |
As you can see, the car battery will only last 58 minutes with an 800 watt load. In comparison, a car battery has 60% capacity of acid-flooded deep cycle battery and only 35% the capacity of a brand new AGM deep cycle battery!
The voltage drop behavior was similar to that of the other batteries, although it was at a much more drastic scale than the deep cycle battery. In some instances, the voltage drop was 0.8 volts per 10-minute session.
Final Thoughts
We learned a lot when we tested 3 batteries side by side on how long they will last with an inverter. Some results were expected, as well as some surprises. For the most capacity, an AGM deep cycle battery will give you 164 minutes of 800-watt continuous power, with a regular acid-flooded deep cycle RV battery coming in at 96 minutes. Finally, as suspected, the poorest performer was a car battery that would only give you 58 minutes of power on the same load.
Tony is an avid camper and RV traveler. He fell in love with camping on his first RV trip with his wife over 25 years ago. Tony loves sharing lessons learned and tips about RV maintenance and safe traveling.