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TV-Battery Question

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I'm not knowledgeable on things electric but, I want to watch my TV while boon docking and don't want to use a gas generator.

I'm thinking.......just use a EXIDE® Nautilus™ Marine Deep Cycle battery 115 ah with an inverter. I could charge it when I drive but my concern is how many hours could I watch TV before I have to charge the battery? (The TV uses 40 watts at 3.5 amps.)

Thanks for your help!

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There are a few factors involved. What else would you be running at the same time? Fridge on propane? Water heater? Lights? OTA antenna with/without antenna booster? Is the TV 12v or 120v (I'm guessing 12v if it's 40watts @ 3.5amps) ? If it's 120v you'll have to account for the inverter overhead (approx. 25watts)?


All of that aside, you really don't want to use more than 55ah's between charges. Given a basic parasitic draw only using 12v systems with only the 12v TV on you're going to be pulling around 5 amps so that would give you right around 10 hours of TV time IF your battery is 100% fully charged and there is no energy loss in your wiring or connections... which there more than likely will be with "stock" wiring. That should get you in the ballpark, but anything else on or anything less than 100% state of charge when you turn the TV on will subtract from your total viewing time. ;)


Realistically, you will only have around half of those ah's available for the TV as the other half will be used up in daily parasitic draw that is unavoidable even when nothing is actively "ON". So, safely, you should be able to go 3 hours of TV and still allow a couple lights and a tiny bit of water pump time without depleting your battery to a harmful level.

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Thank you for the reply.

The TV is 120v 40 watt 3.5 amp and the inverter is 1000 watts. Nothing else running.

3 hours you think?


For a 120v 40watt TV that would be more like .33amps which roughly translates into 3.5amps of 12v DC + 25watts (conservatively for your inverter overhead) so another 2amps for 5.5amps total just for the TV.. however... that doesn't account for any current loss. So yeah.. reasonably, 3 hours you should be good as long as there are no other 12v loads and your battery is starting at 100% SOC. Remember though.. in a boondocking situation you might have some "setup" loads that will tax your battery pretty heavily. Ie., extending your electric awning or slides, etc.


55 usable ah's is really the bare minimum for just an overnight stay without hook-ups or some gen time just to "maintain" your rigs most basic systems. Your battery might not be at 100%, and so on and so forth. Less TV time would be better, but if you need to catch the local news and a favorite show it should certainly be quite doable.


Best advice.. give it a go and see where you land! Everyone's energy requirements and rigs vary so the above are just general information and averages, but 3 hours should be a very reasonable estimate.

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You can also get a portable solar panel and connect it to the battery.


Depending on the size of the panel it will significantly extend your viewing time.


I use a 30-watt panel with a small sealed battery for my trolling motor. It works great and I don't need a large flooded lead acid battery on my plastic pontoons.



Vladimr Steblina

Retired Forester...exploring the public lands.


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