Replacing a battery?

Hey friends, have a quick question about battery usage and how long between recharge.  (I see there have been some other discussions about similar issues, so hopefully I'm not repeating something!)

We have one deep cycle batter in our 24' Coachman. Wondering if you advise replacing it, or this is average use?

Here is our charging/volt reading @battery chart:

11.3 w/o charging

... after an hour on converter charge:
12.5 w/ generator shore power (converter)
12.1 w/o generator

? After two hours on converter charge:
12.62 W/converter charge
12.40 w/o charge

... after three hours on converter charge:
12.86 w/ charge
12.6 w/o

? After 4 1/2 hours on converter charger
13 w/ charge
12.66 w/o charging

(a new battery would read at 12.7 )

5 hours later (water pump  occasionally,  fridge, Water heater at an hour, lights for 20 mins?)
... 11.82 low! ( with RV lights on)

11.4 by morning, "Empty" reading on the gauge (overnight we charged phones and had a furnace kick on for maybe an hour?)

Remember any time you take readings with the charge connected, it is the charger output you are reading, not the battery voltage. You did take a number of readings where it is marked "w/o generator or charger" but there is always a surface charge on a freshly charged battery which must be taken into account, usually by removing the charger an hour or two before reading or turning on and then off of a 12V light for a few minutes and then reading.

But, in your case it would seem that your battery may require replacement. Any reading below about 12.0V is usually considered pretty dead. It takes a long time to fully charge a battery, only an hour or two doesn't cut it. These batteries should not be discharged more than 50% without charging up fully again (12.6V) .... BUT first take it to an automotive/battery dealership and have it load tested. In many cases this is a free service.

Bear in mind that the so-called "marine/starting deep discharge" batteries are a compromise between the two types. A Golf Cart battery is a true deep discharge battery. That said, you may be better off with two batteries in parallel, same voltage but twice the power available but the same 50% rule still applies.

In addition to what Alpha said, if you're taking your "W/O-charge" voltage measurements soon after you disconnected the battery from the charger, you're not seeing an accurate indication of its State Of Charge. Lead acid batteries have to sit for awhile after they're removed from a charger (with no load) to measure their true SOC.

If your battery has been repeatedly deeply discharged and/or allowed to sit for extended periods of time in a discharged state, there's a good chance it has become sulfated and no longer has the same AH capacity. The voltage indications you listed, after pretty low use, could very well indicate sulfation.

You didn't mention how old the battery is, but if it's relatively new (less than a year) I'd check the water, then throw it on a charger for at least 24 hours. If, after doing that, it still drains down quickly, it's likely shot.

Kev 

Thanks Stu and Kevin, good advice. I did take it to an automotive dealer for a load test they just said, ?the battery is good? But needs to be charged. This was before I charged it with the charge readings above.

Good to know that a battery needs to sit for a couple hours after charging to get a good reading. I didn?t know that.

Two questions:
One.) Let?s say the battery is ?Good?  to keep using, if I were to buy a new battery anyway to double the power, it would be stupid to put a new battery and an old battery together?
Two.) Do you have a favorite a brand battery or even type of battery that you would recommend? It sounds like golf cart batteries are a better way to go?

If you put an old (or bad) battery with a new one the old/bad one will limit the charging of the new one. 

If this single 12V battery is the one that came with the RV it is not likely to be a true deep cycle battery.  Most likely a "marine" battery which is a compromise between a starting battery and a deep cycle battery. 

A pair of golf cart batteries from Costco or Sam's Club for under $100 each will serve you a lot better.  You will need a new short heavy duty cable to connect the 6V batteries in series. 

For the cable look a the cables on the battery and there should be a wire size number on the cable, like 2 AWG, or 1/0.  Use that number and go to Amazon.com and search for "2AWG battery cable".  You should get some hits.  Poke around a bit and you can find some in the length you need, probably 12inches or 1 foot. 

Awesome, thanks! I?ll head to Costco. Is the two golf cart 6 V batteries the same as one 12 V battery?

Dean_Reynolds said:

Awesome, thanks! I?ll head to Costco. Is the two golf cart 6 V batteries the same as one 12 V battery?

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Yes a pair of 6V batteries wired in series make one large 12V battery. 

I meant to add this link in my earlier post:  http://www.marxrv.com/12volt/12volt.htm

That link is "The 12V side of life"  It has lots of great basic info about RV batteries, charging and solar.  In the link is a diagram on how to wire a pair of 6V batteries in series to make 12V. 

Keep in mind you will need more space for the batteries.  They are quite a bit larger and heavier than your existing battery.

Dimensions:
Length: 10 5/16"
Width: 7 1/8"
Height: 11"
Weight: 58lbs

Is the 24' Coachman a travel trailer?  If so you may be able to build a new battery box from pressure treated 1/2" plywood to put on the A frame going to the hitch.  Be sure to have holes in the side of the box for ventilation. 

Dean_Reynolds said:

I did take it to an automotive dealer for a load test they just said, ?the battery is good? But needs to be charged.

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The load testers used at dealers and auto parts stores do not correctly measure deep cycle battery merit. 

The numbers you report lead me to believe you have a single stage charger in your RV, which "works" but can take a really long time (upwards of a day or more) to recover a discharged battery.  I'd review the operation of the charger once you have your new batteries installed just so you know how things will behave with good batteries.

Mark B.
Albuquerque, NM

Dean,

Yes, a pair of anybody's GC2 will serve you well, but I will beg you please to do a web search and read "12 Volt Side of Life" before you do anything. 

One thing that has not come up here is that if you deplete a Lead-Acid to 50% (~12.0V terminal at rest), it can take 4 hours to get back to 90% and another 3~4 hours to get to 100%.  This is without any regard for you converter/charger rating.  A bank will only take what it wants.  You can try to get the recovery done sooner, but you risk loosing every light bulb doing it and you will probably damage the bank.

Matt

May I suggest reading my article in the RVForum Library titled  http://www.rvforum.net/miscfiles/Choosing_right_battery.pdf

A pair of GC2 6v golf car batteries is one good choice, but maybe not what everybody needs. You may not even have space for two batteries, in which case a single 12v is the simple answer.

AStravelers said:

If you put an old (or bad) battery with a new one the old/bad one will limit the charging of the new one. 

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Now there are two ways batteries can be wired
GC-2's are wired in series and when you wire batteries this way "TWINS" is the word. you want same make. model. age. capacity. same same ideally sequential serial numbers. You want these batteries as close to identical as is possible.

But when you put batteries in parallel you can mix and match so long as they are all the same type.. IE> Maintenance free valve regulated wet cells

The older battery will in no way limit charging of the newer unless a cell sorts out an I've had that happen on a battery less than a week old.

Edit: Fixed bad Close Quote tag.

John From Detroit said:

The older battery will in no way limit charging of the newer

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It's not so much an issue of "limit".  Batteries of a different age or service life will have different absorption times and depending on the charge cycle you apply, the stronger or the weaker battery will end up being under or over charged which will even further separate their capacities until either the better one is beaten down to match the weaker one or the the weaker one fails.  If they're "close" then this may not be an issue depending on the application but diversion in capacity can happen even with new/matched sets eventually, mixing old and new pretty much assures it out of the chute.  It "works" for a little while but as time goes on the difference will manifest itself.

If one is willing to charge batteries separately then this isn't so much of a problem.  I have a "fleet" of storage batteries I use in the field and sometimes I'll parallel a bunch of them for increased capacity, which works fine.  But being mostly all different ages and capacities I charge them independently so they each see the charge profile they need.

Mark B.
Albuquerque, NM

Thanks friends, I appreciate the links to different articles.  I would up buying two Interstate gulf cart batteries for only $89 a piece!

Looking into my converter now... I have a Parralax 7100 in the RV currently.  Parralax told me it is a dual stage charger with the maintainer stage at 13.8 volts.

Any thoughts on letting this charge up batteries when i'm connected to the genset or if I pull the fuse for the converter and run a normal batter charger off an extension cord?

Thanks in advance!

Mark_K5LXP said:

It's not so much an issue of "limit".  Batteries of a different age or service life will have different absorption times and depending on the charge cycle you apply, the stronger or the weaker battery will end up being under or over charged which will even further separate their capacities until either the better one is beaten down to match the weaker one or the the weaker one fails. 

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As I said. for batteries in SERIES this true
For batteries in parallel you are very simply misinformed

STATE of CHARGE determines voltage
Electricity takes the path of the least resistance and if you have assorted batteries in parallel like water it "Seeks its own level" that is. When you first add the new battery either the existing or the new battery will have a higher or lower voltage. Thus it will either sit there while the other Battery (or batteries) take all the charge current.. Till they are in lock step. Or it will take all or almost all the charge current till they are again in lock step.

From then till battery death they will remain in lock step.

When discharging if one battery for some reason has a higher charge and thus voltage it will provide nearly all the current till they are in lock step.  Same as the low battery gets all the charge or nearly so

Yes there is some internal resistance that might make a difference at very high current rates.

But at Absorption rates.. You will not notice the difference.

So no batteries in parallel can be mixed they form the perfect socialist society Each battery takes charge according to its needs and provides current according to its ability THE old thing about "IT will limit charging" or "IT will signal the converter full up" is bunk 100%

The error is thinking that if you have two batteries in parallel with a 50 amp charge current that the current is divided 25/25 no matter the size or age of the batteries. That's not the case The current (Be it charge or discharge) is divided according to the needs/ability of the battery

Example one pair of GC-2 (makes one 220 amp hour battery) with a 110 amp hour G-29

Will divide that 50 amp load 2/3 1/3 or 33. amps and 16 amps (plus a bit of change on both)

THu they remain in lock step state of charge wise for all time after the first half cycle.

Dean_Reynolds said:

I have a Parralax 7100 in the RV currently.  Parralax told me it is a dual stage charger with the maintainer stage at 13.8 volts.

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That implies it's a replacement, I don't think the original Parallax converters were multistage.

Any thoughts on letting this charge up batteries when i'm connected to the genset or if I pull the fuse for the converter and run a normal batter charger off an extension cord?

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*If* it's a multistage it should run to absorption voltage then sit for a period of time before reverting to float mode.  But if it isn't a multistage you could be waiting a looong time for this converter to bring up a set of batteries.  So maybe before you head out you could exercise the charger and see what it does when connected to shore power.  Not likely an external plug in charger would be much better than a single stage charger in terms of recovery time so for boondocking you really want a multistage that will restore Ah quickly.

Mark B.
Albuquerque, NM

John From Detroit said:

As I said. for batteries in SERIES this true  For batteries in parallel you are very simply misinformed

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So, you're saying that it's impossible for the older battery with lesser Ah capacity to be over charged while the charger is approaching and sitting at absorption point of the newer higher capacity battery.  And that it's also impossible that this overcharging won't have any impact on the weaker battery cycle after cycle.  The charge acceptance/load sharing model you cite applies only to cells with similar capacities and internal impedance.  Batteries of a different age and service life will not have these attributes. 

From then till battery death they will remain in lock step.

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No argument there.  One of the batteries sooner than later.

But at Absorption rates.. You will not notice the difference.

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This is where they will diverge.  Absorption phase is at constant voltage.  The weaker battery will sit at the elevated voltage longer than the other because it's Ah were replenished before the stronger one.  It's this overcharge every cycle that over time will degrade and accelerate the demise of the weaker/older battery.

Since I'm misinformed the reader is encouraged to research and come to their own conclusion.  Lots of similar misinformation as this to be found, especially in battery manufacturer application notes. 

Mark B.
Albuquerque, NM

Non- Solar/ Non Gen chargers??

Ok battery guru's I thought I would post this here since perhaps some of you have subscribed....

We bought our generator thinking that we would use it for AC and that would of course charge the battery as well.  I am finding that at elevation in Colorado we dont need the AC, so now we run the gen just for battery charging.  Solar of course is much quieter but right now I'm not sure I can afford that. Is there another option for battery charging?  What about battery jump boxes?  Thanks in advance!

Dean

Ohh... second question. Sorry, I forgot.

Would it be better to use the the battery charging feature on the generator rather than the Parralax 7100 converter on the RV?

Thanks!

Dean_Reynolds said:

  Is there another option for battery charging?  What about battery jump boxes?

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Even if the battery jump box has some charging facility there's only so many amp hours there, and once those are gone you have a dead house battery and a dead jump box. 

A charging alternative I've used when I had a popup was to charge the (small) house battery from the tow vehicle.  Yes, it's not efficient and you're idling a car engine for a long time for a few hundred watts but I found that to be OK once in a while especially since it saved me from schlepping a generator and gas around.  If this is a daily exercise your best option is probably the genset.  Since battery charging is typically a modest load, a smaller genset (~1kW) would easily handle it, use less gas and weigh less than a ~2+kW you'd need for AC.

Would it be better to use the the battery charging feature on the generator rather than the Parralax 7100 converter on the RV?

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No.  The 12V port usually has a pretty low output (Example, Honda EU2000 12V output is 8A) and not high enough voltage to fully charge batteries unless you run it for many hours.  The parallax will dump 45-55 A or so initially and restore the bulk charge much more quickly.  If it's multistage you'll get a charge restored much more quickly than through the genset DC port.

Mark B.
Albuquerque, NM