is it safe to add a second house battery?

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BigNormitasca

BigNormitasca

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In my 1976 Itasca RV it was originally equipped with one deep cycle house battery to run the lighting inside but I'd like to run an inverter in addition to that something about adding a second house battery to it if I add a second battery in parallel is it safe to use with the original wiring given that there's increased amperage I just want to increase the amount of time that we can run things like the lights without having to run the generator and run a 1500 watt inverter without draining the battery
 
I seriously doubt the original battery was a DEEP CYCLE. more likely a MARINE/deep cycle (Pay attention the the case in this post. MARINE are starting batteries and the use of lower case after the slash means "Afterthought, not main purpose")  These batteries you can safely use 20-25 percent of their capacity.  DEEP CYCLE.. fully 50 percent (half).

Now: Can you safely add a 2nd battery....

IF the existing battery is fairly new and in good condition YES

If it is in need of replacement.. Consider converterting to a pair of GC-2 (6 volt in series so as to make one BIG and I mean BIG 12 volt battery)  like 220 amp hours and you can use half of that.> This is the mininum recommended battry for a 1,000 watt inverter

2,000 watt. 2 pair, 3,000 3 pair and so on.
 
Adding the second battery doesn't alter the amperage the wires carry, but adding (and using) an inverter might. The additional battery just increases the time that the greater amps can be utilized before the voltage drops too low to be practical.

Let's say you add a second battery, or maybe replace the existing single battery with a larger capacity one. Either way you have more amp-HOURS available, but the number of amps drawn at any moment is unchanged.  The lights and the LP detector and water pump don't require any more amps than before.  Now add a 1200 watt inverter. The inverter can draw as much as 110-120 amps at its full 1200 watt output, so the wire between the inverter and the battery(s) becomes a crucial factor.  No other wiring in the RV is involved, however. So, if you cable the inverter direct to the battery(s) with a wire rated for that amp load, you are good to go.  The wire size is affected by distance, so the length of the wire from inverter to battery is a factor is wire size selection. There are ampacity tables online to help with the sizing.
 
BigNormitasca said:
In my 1976 Itasca RV it was originally equipped with one deep cycle house battery to run the lighting inside but I'd like to run an inverter in addition to that something about adding a second house battery to it if I add a second battery in parallel is it safe to use with the original wiring given that there's increased amperage I just want to increase the amount of time that we can run things like the lights without having to run the generator and run a 1500 watt inverter without draining the battery
Click to expand...
Gary gave excellent info.

Some additional thoughts.
--  If you are thinking of a 100 watt inverter to keep a laptop charged, you can just plug the small inverter into the 12V outlet and it should work just fine.
--  Anything larger than a 100 watt inverter needs to be wired directly to the battery, as Gary said. 
 
The original battery is long gone. I replaced it with a new deep cycle battery.  And yes I was planning on Wiring the inverter directly to the battery there's plenty of room in the battery compartment to house the inverter and a second battery.  Thanks for the info.
 
BigNormitasca said:
The original battery is long gone. I replaced it with a new deep cycle battery.  And yes I was planning on Wiring the inverter directly to the battery there's plenty of room in the battery compartment to house the inverter and a second battery.  Thanks for the info.
Click to expand...

It's usually considered a bad idea to mount any electronics in a battery compartment.  This applies to chargers and solar controllers as well as inverters.  The fumes given off by Flooded Lead Acid batteries are very corrosive, and they will shorten the life of any components in the compartment.

There is also an admittedly remote possibility that a spark from such a component might cause a hydrogen gas explosion.

Of course, if you're using sealed AGM batteries, it's a different story.
 
Also most battery compartments are exposed to the elements.  Dust, splashing water when driving, etc.  Inverters don't deal well with water.
 
Multiple batteries in parallel is a standard installation in many rv's. I will be a little more emphatic in ruling out an inverter in the battery compartment. Charging lead acid batteries give off oxygen and hydrogen which makes a very explosive mixture. This is particularly dangerous with an inverter because of the high rate of charge on a significantly depleted battery.

Ernie
 
If the current battery is fairly new. No problem adding a 2nd battery. IF it is getting a bit er, long in the tooth shall we say why not UPGRADE to a pair of GC-2 6 Volt golf car batteries?

Some numbers
Group 24  about 75 amp hours
Group 27/28  just under/over 100
Group 31 about 130

Most of those are MARINE/deep cycle meaning you can use 20-25% of the capacity safely

GC-2  Golf Car 2 in series mane 12 volts
220 amp hours DEEP CYCLE meaning you can use half or 110 amp hours

All amp hour ratings are teh C/20 rate

Zantrex recommends about 200 amp hours per 1,000 watts of inverter

Or one pair of GC-2 per kilowatt  More if you can install it.
 
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