Batteries for RV's

Ideally it would be nice to buy two batteries but with limited funds that isn"t going to happen today.

Would you wire them in parallel or run one down then swap batteries? What if you had two new ones, would you do it different?

Any ideas for a battery? I am looking for cost/effective not top of the line. I understand that I should look for a larger number for Reserve Capacity. Just run a water pump, some lights, nothing big.

A bank of eight 6 volt Deka GC-2 flooded lead-acid deep cycle 215 AH batteries cost $480 dollars -cost at 7 years is $69 per year for 10.3 KWh

A bank of eight 6 volt Concorde Lifeline AGM 220AH GPC-4C batteries cost $1936-cost at 7 years is $242 per year for 10.5 KWh

A bank of eight 12 volt Concord Sunextender AGM 86 AH PVX1080T cost $1640 - cost for 7 years is $234 per year for 8.2 KWh

A bank of five Trojan deep cycle flooded lead acid 6 volt 370 AH L-16s cost $1200 - cost at 7 years is $171 per year for 11.1 KWh

A bank of three Rolls/Surette 6 volt deep cycle flooded lead acid 546 AH cost $1560 - 20 year life
expectancy - cost per year is $78 per year for 9.8 KWh

Average projected life-spans for deep-cycle type use for several battery types:

Automotive cranking flooded lead acid: 3-12 months
Marine flooded lead acid: 1-6 years
Golf cart flooded lead acid: 2-6 years
AGM deep cycle: 2-7 years
Gell Cell deep cycle: 2-5 years
Large golf-cart (L-16 type etc): 4-8 years
Rolls-Surrette premium deep cycle: 7-15 years
Industrial deep cycle flooded lead acid: 10-20+ years
Telephone (float): 1-20 years. NiFe (alkaline): 3-25 years
NiCad: 1-20 years

1) Two sixes in series may or may not be capable of storing more energy then two twelves in paralell. Energy storage is a function of Volts x Amps x Time, kinda like how the utility company charges you for killowatt hours which are indeed Volts x Amps (= watts) over time (hours).

2) Sooooo oo although ITS INDEED TRUE that amp/hrs is additive for paralell combinations BUT NOT FOR SERIES, if the sixes are good heavy duty such as golf cart units rated say 100 amp hours, two in series still equals 100 amp hours BUTTTTT T if you used two twelves in paralell that were light duty wimpy batteries rated at 45 amp/hrs each, that would only equal 90 amp/hrs WHICH IS LESS ENERGY STORAGE THEN THE TWO HEAVY DUTY SIXES.

3) HOWEVER, if you compare two sixes of 100 amp/hrs each for a total of 100 amp/hrs versus two twelves in paralell of 75 amp/hrs each equalling 150 total amp/hrs, THEN THE TWO 12'S IN PARALELL STORES MORE ENERGY

Sooooo one cant say for certain which combination (two sixes in series or two twelves in paralell) stores the most energy unless and until one knows the amp/hrs of each and compares apples to apples.

NOTE the thing is the big heavy duty golf cart type batteries are well built super heavy duty with high amp/hr ratings that indeed store a ton of energy and designed for numerous deep cycle draw downs and recharges and two in series (even though amp/hrs remains the same) would work well for an RV or golf cart etc. Thats how n why if you were to use two leser quality lesser rated 12 volt so called RV/Marine deep cycle bateries, you may or may not have more available energy stored then using the two sixes. GOTTA DO THE MATH

Another consideration in favor of the golf cart series batteries is whether or not you can purchase a 12 volt of identical type n quality n heavy duty construction similar to the 6 volt golf cart type????? ?? The golf cart units are for that specific application which is why they are so good (designed for lots of discharges n recharges) while Im unsure if any use 12 volt combinations which would require them to be of the same quality????? ??

BOTTOM LINE FOR RV USE: The goal in my opinion would be to use what combination STORES THE MOST ENERGY if you plan to dry camp for long periods when you cant charge up the batteries. Again the most energy storage is the most amp/hrs so read the battery specs n do the math (remember amp/hrs is additive ONLY in the paralell) n make your choices. HOWEVER if the batteries get a lot of deep cycle draw downs and a lot of recharges, in that case even if the two golf cart batteries store less amp/hrs energy, they may provide more years of trouble free service !!!!! !!!!! ! Each time a battery is depleted and rechargred it looses part of its life so battery quality and type (deep cycle golf cart etc etc) is another important consideration in addition to total energy stored (which two twelves may well be greater)

If I knew I could buy a 12 of the same quality n type n design (lots of discharges n recharges) as a 6 volt golf cart battery and the addition of their amp/hrs is greater then the sixes,,,,, ,,,then I woukld uSe two twelves in paralell HOWEVER if I cant get twelves of equal quality, I may use two sixes provided the amp/hrs is not drastically less. Problem is Im not sure if any twelves are the same quality as a golf cart rated 6????? ? Anyone know fer sure????

Hope this explains the electrical stuff so you can look at your use (a few long dry camps where max energy storage is needed versus longer life if theres gonna be tons of deep cycle draw down n recharges over the years) and read the battery specs n do the math to decide whats best for your intended use. REGARDLESS IF SERIES OR PARALELL the batteries ought to be matched and in same age n condition n state of charge n specific gravity cuz otherwise the weaker unit zaps energy from the stronger and shes mis matched.

John T Nordhoff in Indiana, retired electrical engineer

Ideally, you should get the two biggest 6V GOLF CART batteries you can find, and wire them in series. Golf cart batteries are designed to hold charges for long periods of time, and are designed to be drawn right down to nothing repeatedly, and bounce back without so much as a whimper. A little more expensive, but money well spent as the "deep cycle" marine batteries you can buy today are absolute crap.

Also consider investing in a "battery tender" or a "float charger." Harbor Freight sells a float charger that I swear by for maintaining 12V batteries over long periods of storage.

BUT....

In my old pickup, I put another battery bracket under the hood, picked up an air conditioner relay and connected the coil to the accessory position of my electrical system. The contacts of the relay went between the alternator and the positive side of the battery. This meant that anytime the pickup was running, I was charging the secondary battery as well as the regular battery.

I also carried a jumper cable so if I ever needed a jump, I could go from the secondary battery to the primary with a single lead.

A friend had an interesting system. He wired a cable with cigarette lighter ends on each end. He plugged one end into his camper and the other into the cab cigarette lighter when he was cruising down the road. He seemed to always have a charged battery.

Note that a 12 volt battery is nothing more than six 2-volt batteries in series. A 6 volt battery is three 2-volt batteries in series. Placing two 6 volt batteries in series is exactly the same configuration as one 12 volt battery, except the individual cells are bigger and its divided into two cases.

Keith

thanks again

Llloyd

If you wanna spring for the bucks, the new AGM batteries offer more energy storage and like ZERO maintenance for the same size package then the older conventional lead acid types.

Its possible to use solid state battery isolators that allow BOTH the engine and coach batteries to charge while driving via the alternator but they allow dry camping discharge ONLY from the coach battery while dry camping so the engine battery does not get depleted. Thats also possible from use of relays or mechanical knife switches. When connected to shore power the campers inverter charges the coach battery.

Sooooo the bottom line is to use deep cycle marine/rv batteries for the dry coach power and if you wanna increase the total stored energy for dry camping, go with two twelves in paralell.

John T Nordhoff in Indiana, retired electrical engineer

Hypothetically speaking if you had one 12v and used it down to near nothing. Switched wiring and used the 2nd battery down to nothing. Take that total time both batteries were used would it be the same if they were in parallel?

Thanks guys.

All batteries will put out more energy when that
energy is used over a longer period of time. So if you discharge a battery in 10 hours, you will get less amp hours out of it than if you discharged it
over 20 hours. When you leave 2 12 volt batteries
hooked up in parallel you get more over all energy
out of the pair than if you used each one individually because you discharged each on over a
longer period of time.

Using the batteries seperatly is better in the case where you have 2 batteries that are a different age. This is when using 12 volt in parallel. That is what I do where I have one
dedicated trailer battery under the hood on a relay that is 10 years old and pretty wipped and
one newer one on the trailer. I use up the truck
one first then unhook the bumper plug and hook the trailer battery back up. If they were both the same age then it would be better to discharge them
together.

John T

I have heard about going with 2 six volts but not really sure about the performance. I just got off the phone with a "battery superstore" and he suggested 2 marine batteries going for about $85 each that have a reserve capacity of 182 min at 25 amps. I then asked about 6 volts and he said that their name brand is also $85 each.

Still baffled as what to do. This is actually for a horse trailer with living quarters and 99% of the time there is no AC hookup so I charge it back at home with a battery charger.

Thanks for the input.

I've been more than satisfied with the two 6 volt. Good luck in your choices.

Fun discussion yall

John T

The first system is a typical 12 volt system and the battery does hardly more than crank the engine. When underway, the alternator does just what it does for a car, it recharges the battery and meets electrical demands. Often a switch (manually operated) or an automatic switch will allow the alternator to charge the coach battery(ies) in the second system if the engine system has become fully charged. The battery that cranks the engine is a plain vanilla 12v battery, and you can buy a nice one at Advance Auto or AutoZone for $39 or $49 when they have battery sales, and you'll have 4-5 years of problem free use if you keep it maintained, clean, and adequately charged.

The second system is that used for camping. It is much preferred to be a deep-cycle battery that takes a slow charge and releases its energy in a slow manner, perhaps over several days. It is normally recharged when plugged up to 120v in a campground or when you return home. On high end models, it might be charged by a solar panel. It should be larger than the average single battery, and is generally more expensive. Far better are two large 6v batteries hooked in series (to make 12v). Golf cart batteries are great. You can get superb ones at Sam's Clubs everywhere. They need to be replaced in pairs or you will have unsatisfactory results. To answer your question, I would never hook up an old battery in series or paralle to a new battery; you'll soon have two bad batteries.

My RV had its engine battery adjacent to the engine, just like you'd find in a truck; and it had a battery tray between the engine and the front bumper where two 6v batteries fit. I guess it would have used two 12v batteries there, if you use those, they would be hooked in parallel. But the six volts batteries will give you much better service. Only the batteries know they are six volts (when hooked in series), everything you get from them and all the appliances are still 12 volt.

Don't skimp on batteries, they'll leave you in a bad way if you go to places without shore power or helpful fellow campers.

For a engine starting battery, I have to agree that a good wet cell in the price range of $50 will get you 4yrs easy. 3 battery's at 12yrs for $150 total cost. However if your in the habbit of total discharging a wet cell starter battery then that battery will be ruined after the first couple times of being flatlined.

A Optima gel cell, about $125 can be continously flatlined and last for 10yrs, so it may be a better buy if you abuse your starting battery.

RV house battery's are another story. The best bang for the buck are Torjan T-105 6v @225amp/hrs, or aka golf cart battery's, about $72eh. Two series T-105's give you 12v @ 225amp/hrs of use. All my numbers will based on the T-105. The T-105 has been around for many years and is known for it's excellant service.

To make a RV battery last for a long time, 10yrs is common, you can not discharge that battery below 50% of it's rating or about 110amp/hr before recharging. That's about 12.05v at recharge time and being fully charged 12.73v. Battery's have to be at rest (no discharge/recharge) for atleast a hour, best is 6hrs, before voltage can be used as a indication of battery state of charge. Using a hydrometer is a better way for telling instant state of charge without having to wait.

From my personal experience with two 12v 105amp/hr deep cycle battery's, I averaged about 2yrs per set. Do not use combination marine/deep cycle battery's as they don't carry the amp/hrs that a good deep cycle battery has.

T-105's will out last, both is amp/hrs use and longivity, any 12v deep cycle battery as the T-105's have thicker plates. Two T-105's weigh about 138lbs where two 12v battery's weigh about 120lbs.

I boondock camp 100% of the time at 9000ft, usually for 6mths at a time, so I really use the battery's hard. My normal daily battery useage is 30amp/hrs per/day, for water, lights, furnace, plus misc items. I've been 100% solar for the past 8yrs, no generator use at all.

This year I'm changing that too where my useage will be 71amp/hrs per day. I added more battery storage for a total of six T-105's but didn't add additional solar pannels. With good PV management I'm going to see if I can't get by with my existing PV's. We'll see!

According to Trojan, the T-105 will put out 32% more useable amp/hrs than the US2200 6v battery sold at Sam's Club. I hate to get caught in the middle of any mfg war but Trojan has never let us down yet.

I can't make the AGM at $200eh pay back the high battery cost.

Also battery's and PV's are taking a huge price jump this summer. There's already many reported shortages of PV's on the market clear into mid 2007. I called several places and they all priced the T-105 at $89 but I found a golf cart parts dealer selling them for $72eh as his shop is out off the beaten path and he uses battery's to get people into the store. T_Bone

Another area that has really excelled in battery's this past few years are the new PWM battery charging alogrythm that regulates the newer rechargers. Aka smart chargers.

With PWM, a battery can be recharged faster, 3hrs instead of 10hrs, with very little off gassing and even during float charging. That means less battery maintance as they don't use but very little water. Before I would add water once per month, now once per year.

What all this means is the guys that want to use generators for recharging battery's can now almost fully recharge there battery's in less than 2hrs of run time, depending on battery charge state, thus saving a huge amount of fuel used VS using the old method.

Another charge regulator, MPPT for PV regulation is promising more watts out of the same PV's by using a different alogrythym.

MPPT's are fairly new to the market and literature is pushing sales and not releasing enough therory to tell if MPPT is that huge of a leap over PWM recharging.

One thing that caught my eye on MPPT is, maximum benefit is tempature dependant, ie; the colder the PV's and ambiment conditions the higher the gain. MPPT claims 32% max wattage gain under ideal conditions.

For RV use, I'll reserve my comments for MPPT conntrollers until there field proven to be a benefit.

For RV use, PWM is well worth changing a good old style regulator for the new PWM regulator. About $55 for a 10a CC, Morningstar Sunsaver, for PV use.

If you have a newer RV or newer RV convertor, you can add the smart charger (part) for about $30. Well worth the cost. If I was recharging via genset, I'd replace my working convertor with a new PWM 80amp charger, about $225, as I would save that in fuel alone.

There's huge benefit for battery longivity with the new PWM chargers. If the battery's don't short the plates from road viberation, I could see maybe 15yrs out of T-105's.

T_Bone