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Old 02-10-2019, 08:20 PM   #1
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Need dual batteries in new 24' travel trailer?

If I could accurately determine the usage we will have with our new 24' trailer I could calculate the AH required for that usage. I cannot however anticipate how we will use the trailer with any certainty. Most usage will be where electricity is available or with an inverter / generator. Occasionally there will likely be a night or two without electric hookup during which we would have appliances on gas, use interior lights for 3 or 4 hours and watch the news on TV morning and evening. I suspect many TT owners have similar occasional electrical usage. The question is, should I add a second battery in parallel with the first or stay with one battery and avoid the added maintenance issues on an unneeded additional battery?
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Old 02-10-2019, 10:13 PM   #2
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I assume you have one 12 volt battery. Is it a true deep cycle battery or a marine battery? How many amp hours is it?
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Old 02-11-2019, 04:30 AM   #3
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You probably have 1 group 24 wider battery. I would replace that battery with a larger battery with more reserve power like group 29/31.

If you really want to go nuts you could buy a very expensive but much better Li battery for $1,000.

My last trailer that I bought new I asked the dealer to install a group 27 battery. Bigger battery box was needed so my replacement battery will be a group 29/31 size.
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Old 02-11-2019, 05:17 AM   #4
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If you have the room you can't beat 2 6V golf cart battys in series. They are about the lowest $/AH/cycle you will find. Sam's Club or Costco about $170 for a pair... and they are True Deep Cycle not combo like those marketed as marine / RV. GCs will last if taken care of. See
https://marinehowto.com/what-is-a-deep-cycle-battery/
If you prefer AGM they are about 2X $
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Old 02-11-2019, 06:07 AM   #5
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Iíll second Winemaker2 as I did exactly what he said. A couple of things to consider; a good smart battery converter/charger and replace your incandescent light bulbs with LEDís. If you have an IOTA converter/charger you may be able to purchase a smart charger module. The module is cheap and work very well. https://www.iotaengineering.com/IQ/#!/
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Old 02-11-2019, 08:05 AM   #6
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Of Course it Varries

Of Course it Varies.
I have a Kodiak Cub 21 ft TT. It came with basic low end appliances. I have 200 amp/hrs of sealed AGM batteries. The TT came with 60 amp/hr flooded cell marine battery.

I can camp for 5 days if the furnace is not needed and still have more than 1/3 in reserve. That makes 30 amp/hrs per day.
As a general rule of thumb target using 50% of capacity for flooded cell batteries. 60 amp/hrs gives you 1 day plus reserve.

True deep cycle batteries can tolerate deeper draw. AGM batteries can be routinely be drawn down lower with no loss of performance.

Higher end appliances typically use more 12 volt power for various controls. If you have auto switching from 12 to 115 volts the control devices will have higher parasitic load.
If you have incandescent lights, they use 5 times as much power. If you use an inverter to power 115 volt devices from battery, the inverter can draw significant power. Ö and so forth.

Staying for more than 1 day on battery power would benefit from more than 60 amp/hours. Using the furnace will also benefit from more. A 100 amp/hr AGM class 31 would greatly enhance your dry camping experience. With sealed AGM you do not have to worry about monitoring water level and spilled or sprayed acid on everything. Deep draw AGM's can go flat a few times with no noticeable performance loss. AGM's are worth the extra money for TT use.
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Old 02-11-2019, 08:11 AM   #7
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Two 6V golf cart batteries is ALWAYS a good bet !
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Old 02-11-2019, 10:21 AM   #8
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I put on 2 6Volt golf car batteries from Costco, (about $200 with core charge, take 2 old ones in and get that back), and got 2 GC2 battery boxes from Batteries + for about $15 each plus one jumper wire for $8. I can easily go 2 days using furnace, TV, CPAP etc. and still have over 50% charge left. Run your generator a few hours on the third day to top them off.
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Old 02-11-2019, 08:39 PM   #9
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The answer is yes. You will not be wasting your money with the addition of a second battery. However, it needs to match the existing battery or one will pull down the other. And that is a waste.

Even a brand new battery on a coach just delivered may have been stressed, if it has not been correctly charged. A wet cell or AGM battery can only be discharged to 50% (12.2 volts) without shortening it's recharge cycles life.

Suggest you replace the existing battery with a matched pair of 12 volt or 6 volt batteries. Your choice depends on the available space to mount the batteries. Cost for two 12 volts is about $300. Cost for two 6 volts is about $450. Lots of variability in original pricing. Walmart can save you about $100 and provide warranty coverage across the US.

The alternative is to purchase one of the lithium direct replacement cells. You will need to possibly upgrade your battery charge converter to lithium charge capable. The Progressive Dynamics converters are now sold with a Lithium option. Cost for this pachage is about $1250 if you do the labor. Advantage is one battery and lighter weight. The Lithium can be discharged to 20% capacity, recharges faster and has a longer recharge cycle life. However, if you travel in cold weather, it may need to be mounted in the coach. Lithiums do not like cold weather. Look at Battleborne and Viper brands.

Contact the battery experts for more information and advice.
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Old 02-11-2019, 10:51 PM   #10
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You can also get two 6 volt deep cycle (golf cart) batteries at 215 AH each for about $200 at Sam's Club, Costco, or Batteries Plus Bulbs.

Here's a link to the B + B 6 v batteries: https://www.batteriesplus.com/productdetails/sligc110
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Old 02-12-2019, 08:36 AM   #11
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Remember those crank emergency radio's that you crank for 60 seconds and you can listen to the radio? The ones that also had an incandesent light.

I played with one as a kid. Anyway, you crank for 60 seconds you can listen to the radio for 60 seconds or use the incandesent light for 5 seconds.

That told me that lights take a lot if energy.

LED lights take about 1/7th the energy as the incandesent lights.

I have not tried a emergency crank radio that had an LED light just yet.

Anyway - I agree with changing the lights to LED.
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Old 02-12-2019, 10:20 AM   #12
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50% a rule of thumb or limit to avoid abusing batteries

Quote:
Originally Posted by PKI View Post
The answer is yes. You will not be wasting your money with the addition of a second battery. However, it needs to match the existing battery or one will pull down the other. And that is a waste.

Ö

A wet cell or AGM battery can only be discharged to 50% (12.2 volts) without shortening it's recharge cycles life.

Ö
PKI makes a good point. For long life, fast charging, and maximum available capacity the batteries in a bank must be the same brand, type, and size.
To get more capacity cheaply, buy a duplicate of the one you have, a second battery box, and a pair of heavy connection cables.

There seems to be a widely believed myth that lead/acid batteries last twice as long if you only discharge them to 50% of capacity. The reality is they can be recharged twice as many times. Of course that means you only have half the capacity on each charge. Using 50% of your battery banks capacity is a good rule of thumb. It reduces the possibility damaging the battery by drawing it down flat. It provides reserve capacity for when things don't go as planned. But you will get the same number of amp hours of storage life out of either method.

Charging to 90%. Discharging to 10% is a typical test procedure. A good battery design may get 300 charge cycles before capacity drops to 80% of new.
Charging to 90%. Discharging to 50% is sometimes tested by manufactures as well. Usually the test yields about twice as many charge cycles. Of course you only get half as much storage capacity.
The biggest contributor to the deterioration is the distortion of the electrodes each time the battery is charged. It isn't the number of charges that matters, it is the amount of charge that distorts the plates.

Starting batteries are the most sensitive. The shape of the plates is intricate. The shape changes gradually loosing surface area with each charge and thus loosing cold cranking amps capacity. Drawing it down flat will pretty much destroy the intricate pattern on the electrodes.

Deep draw flooded cells are designed to be drawn down to 10%. Drawing them down flat damages the plates, but does not destroy them. Some are better than others. Having a reserve is an excellent strategy to avoid early failure.

Deep Draw AGM batteries are also designed to be drawn down to 10%. However, drawing them down flat does very little damage. The reason is the chemistry in the AGM battery runs out of charge in the electrolyte before it runs out of lead on the plates. An accidental full discharge makes very little difference to the life of the AGM.

On the other hand, AGM batteries are sensitive to overcharge or charging too fast. Both conditions will cause the AGM battery to vent. Loss to venting is permanent. It cannot be reversed. Most modern charger/converters in TT's and MH's will not charge too fast. They are voltage limited. Some can overcharge a little. They may not lower the fast charge voltage from 14.6 to 13.6 volts soon enough or switch from 13.6 to 13.2 maintenance charge soon enough. However, that loss is minimal and accumulates gradually. No big catastrophic failures here.

Deep draw AGM are optimized for applications like TT's. A good converter/charger and shore power or generator for charging are ideal for long life. Accidentally leaving the battery disconnect on for 3 months of storage will not kill it. There is less maintenance. AGM's won't spilled or spray acid on adjacent equipment. They do not vent explosive hydrogen gas as a part of their normal charge cycle.

Full timing with lots of boondocking or dry camping may benefit from gulf cart batteries. They generally are flooded cell, deep draw, and designed for fast charging. Buy them at discount prices, maintain them properly, and you will get good return on your money.
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Old 02-13-2019, 06:48 AM   #13
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Thanks everyone - Good input. What to do with a new 12 V?

In response to the question of what I have on the TT...I have not lifted it out of the box to determine...I will ask my RV dealer as the trailer is new (Dec.) and they likely have a single type they use. Knowing the answer to that question then I will need to determine whether to pair a second in parallel or go for two 6 V golf car T105's in series. If I decide to use the golf car type, is there a good use for the battery I have in the trailer...on charge but never drawn down. It would be a waste to set it aside or to recycle it while still new. Thanks again for all the good input!
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