How Long Will a Deep-Cycle Battery Power a TV? What You Need to Know.

When I first built my battery bank, I naturally wondered just how long I could power my TV with some deep-cycle batteries.

Maybe you’ve got one at home and you’re in a power outage, or you plan on taking a camping trip and you’re just curious.

Either way, I set out to find the answers.

A 100 ampere-hour deep-cycle battery with a power inverter can power a 32″ LED TV at 35 watts for 34 hours, or a smaller 20-watt TV for about 60 hours until the battery is fully discharged. 

Below, I will cover the 4 main considerations to arrive at a conclusion to this question for any size TV and any size deep-cycle battery. By the end, you should be able to plug your own numbers in to see what you’re working with!

If you’re in a hurry, just click here for the charts to get a good estimate.

Let’s get started!

1. How Many Watts Does a TV Use?

Small TV’s with 15”-20” screens in the LED and LCD categories will use about 15-26 watts.  Medium sized TV’s with 21”-32” screens will run about 26-70 watts. Larger TV’s from 32”-55” will be about 55-150 watts. 

You can test your TV’s power usage with this nifty device seen here on Amazon. Trust me, once you get it, you’re going to be testing different things around your house out of curiosity! 

LED TV’s will generally use about ⅔ less energy than an LCD TV of the same dimensions.

CRT TV’s, which lost popularity in the developed world over a decade ago, will run anywhere from 65 watts to 120 watts from a 15” to a 24” screen.

Plasma TV’s, which are also antiquated in the developed world, are energy hogs and will run 150 watts to 300 watts easily.  

In the examples that we’re going to use, I’ll be picking TV’s with watt ratings of 20, 50, and 150. 

2. How many Amp Hours Does a Deep Cycle Battery Have?

The term “deep-cycle” refers to the internal design and chemistry of the battery regarding its use and not its amp-hour capacity.  They have thicker lead plates with less surface area to allow for a longer and slower discharge. Deep-cycle batteries typically come in sizes of 100, 90, 80, 65, and 55 amp-hour ratings. 

Of course, you’ll find some deep-cycle batteries with far more and far less than the rates mentioned above.  

Without getting complicated, the amp-hour (AH) rating gives an idea to the user about the capacity of the battery.  For instance, a 100AH battery should be able to give 1 amp per hour for 100 hours, or 2 amps per hour for 50 hours. 

However, the higher the draw, the lower the AH rating.  Don’t worry, we’ll get to that in a minute.

In the examples that we will be using, I’ll be looking at three 12-volt AGM (absorbed glass mat) batteries with 100, 80, and 55 amp-hours.  I’ll also take three 12-volt flooded batteries with 105, 90, and 65 amp-hour ratings. Finally, I’ll look at what two 6-volt GC2 golf cart batteries could do if hooked in series with a rating of 215 amp-hours. 

3. What Size Inverter do I Need to Run a TV with a Deep-Cycle Battery?

You will be able to easily run modern television sets along with an accessory or two (game console, DVD player, etc.) with an inverter with 800 peak watts.  When powering your delicate electronics, it is best to use a pure sine wave inverter instead of a modified sine wave inverter for cleaner and more reliable power. I have a link to a nice one on Amazon.

I have used a modified sine wave inverter when the power has been out, and haven’t experienced any damage to my devices.  That’s not to say it can’t happen, though.

When using a modified sine wave inverter, which are about 25-50% cheaper than their pure sine wave counterparts, I do experience harmonic distortions with the TV and it will make a sound at an odd frequency even when the volume is down.  Turning the volume up tends to drown out the noise.

When using a power inverter with a battery, you need to keep in mind that you’ll probably experience about a 15% loss of efficiency when powering your devices.  It just comes with the territory as the power inverter changes direct current (DC) battery power into alternating current (AC) power like from your wall outlets.

In my examples, I factored in this 15% inefficiency (or, 85% efficiency) factor. 

4. Peukert’s Law

Finally, we need to remember Peukert’s Law if we want to get an accurate prediction about how long our deep-cycle batteries can power a TV.  

Peukert’s Law basically says that the higher of a draw you place on your battery, the lower the capacity of the battery will be.  

So, that 100AH battery that can give you 1 amp for 100 hours will likely only be able to give you 50 amps for 1 hour and 15 minutes until the battery is completely discharged.  It’s effectively lost AH capacity based on the higher load.

Conversely, batteries can increase their amp-hour ratings at a smaller discharge rate than was used when they were manufactured and tested.  

Deep-cycle batteries are generally rated at a 20-hour rate, or how many amps per hour can be given for 20 hours until the battery is dead.  

So, 100 amp-hour battery can provide 5 amps for 20 hours.  If you were to use less than 5 amps, you would have more than 100 amp-hours.  The amount can be estimated (since these things aren’t linear) but not truly calculated unless you test each battery.  

Just know that you’ll reduce your AH rating at a higher draw than the 20-hour rate, and you’ll increase your AH rating if you stay below it. 

Peukert’s Formula for calculating the time of a battery:

Battery Time = 20 ((AH / (Amps Drawn * 20))^k)

  • 20 (both) = Hours the battery was rated at
  • AH = Rated Amp Hours of the Battery
  • Amps Drawn = (watts of TV / 12-volts / 0.85 inverter efficiency factor)
  • k = Peukert’s Constant ⇒ 1.1 for AGM and 1.2 for Flooded batteries in this example

Example of Calculating How Long a Deep Cycle Battery Can Power a TV:

I’ll only do this once, as this can get pretty boring, but you’ll be able to see how I calculated all the numbers and you’ll be able to do the math yourself with your own TV and battery by substituting your own numbers!

Let’s find out how long a 100AH AGM battery can power a 150 watt TV below.

  • 150 watt TV / 12-volts = 12.5 amps.  (watts = amps x volts)
  • 12.5 amps / 0.85 efficiency of inverter = 14.7 amps needed from the battery to overcome the 15% loss of the inverter and still provide 12.5 amps to the TV.
  • AGM battery will have a 1.1 Peukert Constant in this example.
  • 20 (((100AH / (14.7 * 20))^1.1)) = 6.1 hours until a 100AH AGM battery is fully discharged.

How Long Will a Deep Cycle Battery Power a TV Results

100 AH AGM90 AH AGM55AH AGM105 AH Flooded90 AH Flooded65 AH Flooded
150-Watt TV6.
50-Watt TV20.415.710.621.671812.2
20-Watt TV5643.82965.254.236.7
Time in hours.

What if I have Two Deep Cycle Batteries?

If you have two 12-volt deep cycle batteries, you can hook them up in parallel to increase their overall amp hour rating but keep the voltage the same. 

To hook them up in parallel, you would need to join the positive terminal of one battery to the positive terminal of the other.  Then, you would join both negative terminals together. Finally, you would run your inverter off of the negative terminal of one battery and the positive terminal of the other battery to complete the setup. 

If you have some GC2 golf cart batteries, you would need to hook them up in series since they are only 6 volts each.  When hooked in series, they will keep their AH rating but will double in voltage. 

To connect in series, you simply connect the positive terminal of battery #1 with the negative terminal of battery #2.  Then, run your inverter off the negative terminal of battery #1 and the positive terminal of battery #2.

Quick warning: Never introduce a weaker or older battery to a newer one, as it will degrade the newest one quickly to the level of the used one. 

Robert Van Nuck

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

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