100w inverters are around $10. An inverter only draws as many watts plus around 10% that you're using. If you're going to mount one in a boat, I'd get something decently sized to run other appliances. A 400w will run most things and they are still very cheap.
A TV that draws 40 watts will run on a standard 75 amp hour deep cycle for around 10 hours til the battery reaches 50% and it's time for a charge. If you're charging off the boat alternator... it won't fully recharge forever.
If you're smart and purchase an AGM deep cycle battery to run the inverter.. Like an Optima Blue Marine 75 amp hour deep cycle.. They are good to around 80% discharge and fully charge in 2-3 hours, not all day like a lead acid. They can be had for around $200. TV runtime @ 40 watts?
17 hours.
Really, what it comes down to is do the math. Add up all your watts used. How long do you watch TV for each day? What else do you use? Radio? Does it have an AMP or is it just a head unit? A standard agm deepcycle 75amp/hr battery can easily last all weekend with LED lighting and modern electronics. You gotta figure you're only going to be using most of the electronics at night anyways.
Average anchor light = 10w (for 2mi vis). LED anchor light = 1w. The difference is 10 amps of draw for all night or 2.
Lets say you use 4 hours of power past sunset til you sleep (6pm to 10pm) and I'll be power greedy using modern electronics.
LED LCD TV 55w includes inverter overhead = 18 amps
Small LED mood lighting.. 1 amp
Small fan to move some air? 4 amps
Blender to make sexytime drinks? 1 amp?
25 amps used (with anchor light) at night out of an available 60 amps from a $200 AGM 75a/h deep cycle til the day time when you motor and it recharges.
So yes I'm bored but in otherwords...
Don't worry about watching TV and the battery going dead. If you have a good "house" battery... ie.. second battery.. you'd have to run some serious crap for hours to drain it.. like A/C. If you have A/C and want to run it all night.. don't throw more batteries at it that's dumb. Get:
http://www.yamaha-motor.com/outdoor/pro ... specs.aspx50-60db. About as loud as a conversation between two people. To get an idea.. just sit inside your boat and close the hatch. Have two friends talk outside on the swim deck in normal inside conversation tone. That's what you'll hear. You won't hear it over the A/C. The days of a generator waking up the neighborhood are gone.