Just bought a 3 horse with an LQ equiped with two 12 volt batteries.  We do mostly day shows where we spend the entire day hanging around the trailer.  The trailer has a radio (car radio) that we use but other than that not much 12v stuff being used (it's day time so no lights).  Thinking about getting a 12v fan and maybe a 12v converter for the tv for a daughter that doesn't show but likes hanging around the trailer and taking care of her Special Needs brother in the trailer.  The location that we park the trailer does not make it easy to plug it in when it is stored...in other words it would need to be moved to be charged.  Not fully understanding the capacity of the batteries I have some quesition.

1.  Is there a decent battery monitor that could tell me the status of the batteries?

2.  If we were using a radio all day, fan for a few hours, and tv for a few hours how long would the batteries last?

3.  How long should it take to charge the batteries if we plug in?  The batteries have a dedicated charger.

4.  Haven't got the converter for the tv yet...will it take a lot of power?

Thank,

Mike

Hello Blackcows...

I'll take a shot at your questions

Yes.. there are a multitude of battery monitors.  But they all use voltage to determine the state of battery charge.  You can save a bunch of cash with a digital multimeter that can do other jobs.

All the answers to your other questions begin with "Depends: ..."

Know that all batteries deteriorate with age and use.  If you look at your batteries they will have an amp hour rating.  This is the number of amps the battery can deliver for X  hours.   Roughly, a 100 amp hour battery (in fully charged, brand new condition) can deliver 20 amps for 5 hours or 10 amps for 10 hours or 5 amps for 20 hours. 

So there's your starting point.  Then figure how many amps all the various appliances will draw from the battery.  Then divide amps drawn into the amp-hour of the batteries for the number of hours you can operate them.

Do the reverse for the battery charger.  How many amps can the charger deliver?  Divide the charger amps into the battery amp-hours for the time it will take to charge the battery.

Again ... The "Depends:"  Large charge amps will charge faster but the battery life suffers.  Large amp draws will shorten battery life and reduce total amps available. 

A lot of details have been glossed over but this is the general idea of battery power.

Hoss gave you a good basic lesson.

You might also consider

How far do you drive to your shows. Your truck may provide enough charge to top off the batteries. A 4 hour drive to your show and 4 hours home gives an 8 hour charge, which may be enough.  Across town 15 minutes isn't going to do much.

I find the kids turn on lights even in the day and leave fans and radio running while they are gone etc.  Colder months, your furnance fan runs off the batteries. In the summer the A/C needs 120v. So you will need a generator or shore power hook up to run it.

Correction on wording, 12v DC to 110 AC is an inverter, not a converter, (long day, sorry).