New trailer to be delivered. Do I ned Battery if I have hook ups?

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Dec 29, 2012
Hi all again,

Well im about to have my fifth wheel delivered to RV park. A friend of mine said to make sure I have battery ready to instal. I said its ok cos I will have it connected to power from park. He said you will still need Battery to operate slide outs. Is this true? Or is he pulling my leg? I thought it would already have battery cos how else you going to get trailer brakes to work?
If I need a new Battery what is the best value for the money out there and should I get 1 or 2? Pros and cons please.


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Yes. You need batteries for the on board 12V system to function even though there is hook ups. The on board charger is not suppose to be the only power supply and requires batteries for proper operation.
Oh no! More money... This thing costs more than me ex wife!!! But it sure feels better...
Thanks for the heads up. Do you have a preference on brand of Battery? Where do I get good value?
Any good RV deep cycle battery will work. Don't get the marine batteries. Personally I prefer a lead acid battery and would most likely buy a WalMart battery. Being there is only about 3 companies building all of today's batteries. (Exide, Johnson Controls, and another one... CRS moment)
Buy a decent digital voltmeter (maybe $30) while you're at it. Don't waste your money on a $12 meter, and you don't need the $100 meter... yet.  ::)
If you are "ALWAYS" connected to shore power, ONE average maintenance free deep cycle will work. I wouldn't go too expensive on the battery unless you start to do a lot of camping where you have limited power. Then I would spend the extra money and get two good batteries.
I just replaced the Interstate battery in my 2007 park trailer this year with an RV/Marine battery from Wal-Mart this season.  The Interstate lasted 5.5 seasons.  We will see how long the Wal-Mart one lasts!
Since you will stay connected to park power, get a modest size marine 12v battery from Walmart. That will be enough to stabilize the 12v system in the RV and provide a bit of interim back-up power when and if needed.

Be sure to check the water in the battery cells every few months. The continuous charging will cause it to evaporate and the battery can't function without it. Get a gallon jug of distilled water from the grocery store to use when needed.
Last week I called Progressive Dynamics and spoke to a tech about using the PD4045 converter in my TT while disconnected from the battery, yet plugged into shore power or my generator. He said it was no problem and wouldn't harm the converter.  :-\

The reason for my question was that occasionally I use a remote charger to equalize the battery bank, which is best done with the batteries isolated from any load.  I never called on the converter to handle any large loads, but for the things I used it for it worked flawlessly. The cooling fan never cycled on either.

Oh, and I should add that with the battery disconnected, the output of the converter remained at a steady 13.5 volts. If it had been putting out the maximum charging voltage (14.3 volts) I would have been leary about using it that way.

(edited to correct typo and to include additional info)
If this is a new RV (and it sounds like it is) I find it hard to believe that a dealer would sell you this RV without a battery or anything else that it needs to operate. Do you have things like a drinking water hose, a sewer hose and such for hook up at a RV site?
I find it impossible to believe a dealer would sell most trailers without a battery, THE EXCEPTION is very small trailerx generally 2,000 punds or less.

The reason: A dealer has an obligation to sell a vehicle that is SAFE, and if your trailer is large enough to have it's own electrically oeprated breakes Then, by law, it has to have a break-wway device that locks up said brakes should it ever part company with the tractor (Tow Vehicle) in a non-conventional manner (Example at 60 mph) and that absolutly REQUIRES a battery on the trailer.

Of course if it's too small to need brakes, Then Well... My first trailer did not even have a 12 volt system, I added it.

2nd trailer has some 12 volt lights, but they were owner added by the prior owner.


As for "Do you need a battery WHEN PARKED" with hookups.. Depends on your converter, Anything made this century (2001 on) no you don't.  If it has a Magnetek 6300, you need either a battery or a "Battery Simulator" (Hardening condenser)
ironrat said:
If this is a new RV (and it sounds like it is) I find it hard to believe that a dealer would sell you this RV without a battery or anything else that it needs to operate. Do you have things like a drinking water hose, a sewer hose and such for hook up at a RV site?

X2 I was hoping someone would say this before I got to the end of thread so I didn't have to.  ;D
What John said. If your 12 v appliances work when plugged into shore power or your trailer connector power, then you don't need a battery. HOWEVER, when traveling, your electric brakes will not work if the breakaway switch activates.
Get a battery.
Mopar1973Man said:
Yes. You need batteries for the on board 12V system to function even though there is hook ups. The on board charger is not suppose to be the only power supply and requires batteries for proper operation.

Wrong, that is why it is called a "Converter" and not a charger. As stated elsewhere, it is designed to deliver regulated 12vdc without a battery attached. But you should have an on board battery for at least towing, also most newer Refers need 12vdc for control power even when shore power is available. So, no battery, no cold beer during a power outage because the fridge will not switch to propane.
It depends ...      ;D 

In our 99 coachmen Mirada with a Magnetec converter, the manual called for having a battery connected.  With the Progressive Dynamics converter we have in the Southwind, as a previous poster said, you can operate without a battery.

And as Gary said, nice to have a battery for the short term needs even if you are going to be plugged in most of the time.  And as stated above you would need 12VDC to operate frig, water heater, furnace etc on the road.  Opinions will vary but yes we operate any and all of the above going down the road as required.  And probably for trailer brakes also.

You don't have hookups traveling down the road to any given destination and a battery is essential for the break-away braking system should the need be there!!!!

Some converters will operate fine without a battery but some are just poor suppliers of 12V and require a battery to filter their output and provide a clean 12V. As mentioned elsewhere, the PD series seem to do fine with no battery, at least in the short term..... Others have mentioned the need for at least 1 battery for use during power outages to maintain the fridge, hot water, perhaps the furnace, etc even though they can and do operate on propane.
This is a bit confusing. If you need a battery then what is a Converter? a charger only? If so why not call it a charger? If it is a converter then what does it convert if you need a battery? I thought a converter took 110 volts and converted to 12 volts as well as some had a battery charger also.
It does both.  A good converter like the Progressive Dynamic series will provide a steady DC voltage regardless of the load on the converter.  The output is well regulated, which means the voltage stays the same regardless of the load on the converter.

When you hang a battery across a well regulated converter, it charges up to the converter's voltage and then just sits there, not doing anything unless the converter stops working, like during a power outage.

The voltage from less regulated converters (and chargers) change with the amount of current drawn from them.  Their voltage starts out high when there's little or no load, then drops as the load increases.

These are more dependent on batteries to supply some current to heavy loads.  The battery charges when the voltage is high, then supplies extra current when a heavy load makes the converter voltage drop.  Without a battery you'd see your lights flicker every time the furnace fan or another heavy load comes on line.  It's also possible for the voltage sags to reset the circuit board logic in your refrigerator, water heater, etc.

The other problem is a poorly regulated converter usually overcharges the battery when there's no load, then undercharges when a load is applied.

A third kind of converter has no output filtering at all.  It provides pulses of current, not a steady DC voltage.  These rely on the battery to act like a filter, absorbing the pulses and returning the smooth DC voltage needed by circuit boards and other electronics to function properly.  These are also poorly regulated, and have the same propensity to overcharge the battery when you're drawing little or no current.

So whether you can get by without a battery depends entirely on what kind of converter you have.  Some will work fine without a battery, others won't and can damage sensitive electronics if a battery is not available to filter their output.

And even if you're parked in one place, it's always nice to be able to keep some lights and your refrigerator running during a blackout.
Thanks Lou!!
With the different type converters you have described is there some designation on a given converter to understand what type convertoer one has?

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