Upgrading battery bay

In order to boon dock more and rely less on our generators we need more than the 230 Ah we get from our 2 Interstate GC2 batteries.  The problem is where to put them.  Our battery bay is in our stairwell.  It is only large enough for 2 batteries.  I've looked at a using one of the motorhomes bays but hate to give up the storage.  I've thought of Lithium but I'm not sure I'll be RVing long enough to justify the cost.  The batteries are under one of the entry way stairs.  The way it's designed the batteries only fit one way, side by side, in what I believe would be referred to as North South orientation.  Looking at the bay, it appears that cutting open the bottom of the bay and then extending the floor would create enough room to place 4 batteries in an East West orientation.  Has anyone ever done this? 

Alternatively, I would have to use the bay closest to the entry door.  What I don't like about this, in addition to the loss of storage space, is the added cost of wiring.  I could probably build a strong enough platform for the batteries, but I would not be comfortable running the wires to the converter.  Also, with my limited skills if I built a platform for the batteries, I would have to make it out of wood.  I have no experience with metal fabrication.  If I have the work done by an RV facility, the added cost might just offset the cost of lithium batteries.  Three 12 volt lithium batteries would fit under the stair and wiring would be relatively easy.  But the cost of three 100 Ah batteries, even Costco Lions would be close to $2,500.  Four interstates might cost $500 leaving a significant amount of money for modification to the bay. 

I've looked at this before but at the time we had a gas electric RV refrigerator.  Since installing our 12V refrigerator, battery power is critical. 
 

Find a welding shop, preferably a one man show. Tell him what you need and I bet he could fab you something out of aluminum at a reasonable price to hold the four batteries.  Definitely cheaper than the $2,500.

Josh

I had a 2002 coach with that battery location/limitation and solved it by placing an additional battery in an adjacent bay.  No major cutting needed - I just routed the battery cables thru a 1" hole drilled in the side of the bay.  The single 12v Group 27 I added gave me an extra 100 AH, about a 45% increase. A Group 31 would be about 50%.  For our needs, the extra 100AH took us from barely adequate to comfortable.  Battery cables were about 30", so not really excessive in length.  I mixed battery types too, not optimal but I felt reasonable under the circumstances. Not something I would recommend for battery amateurs, though.


Your first step is to figure out how much more amp-hour capacity you need.  Then figure out cost-effective and space-effective ways to achieve it. Lithium may well be a reasonable solution, since you get more usable AH per battery. 


Have you looked at the available height in your step battery box?  There are slightly taller 6V GC batteries that could yield an extra 15% and might not need any changes.

One thing to keep in mind if you do use a storage compartment is to vent it if you use lead acid flooded batteries. Doesn't need to be fancy, just good air flow.

Also if there is any electronics such as inverters I would make sure it is well sealed off. You do not want any fumes near them.

The shop I would likely use is good but pricey.  They do excellent work.  Unfortunately they are booked until after Labor Day. 

I have never followed the path of the cables from the battery.  My guess is they go to the converter which is closer to the bay I'd use.  If so and I could reroute them with existing cables and then just buy the shorter cables to connect the batteries.  I really don't like the current location and moving the batteries to a bay solves a few problems.  While I haven't worked with metal fabrication, I'm pretty sure I could build a secure wood platform.  Is there a downside to using wood with lead acid batteries?  If so, I would go with AGM's which would also give me more options. 

Haven't thought about venting.  Guess that's only a problem with lead acid batteries. 

Lithium batteries aren't outrageously expensive, considering you can use 100% of lithium's rated capacity vs. 50% of lead acid. In other words, two lithium batteries deliver about the same amount of usable storage as four lead acid batteries and they'll fit in your existing battery tray.  Another benefit is lithium's voltage remains constant throughout the whole discharge cycle, they don't fade out like lead acid.

If you're an Escapees member, Battle Born offers a 15% discount, lowering the price to $850 each. I hear if you pick them up at their Carson City factory they'll give a further discount for the free shipping you won't use.  BTW, it doesn't look like Costco is carrying the Lion battery any more, at least it's not on their web site.

I haven't ruled out Lithium since that eliminates a fair amount of work and the cost to enlarge or move the bay would offset some of the cost of Lithium.  But would I also need to change my converter.  I'm beginning to regret I didn't do that when I replaced the refrigerator. 

As an aside, the reason this issue came up again is because of our new 12 volt refrigerator.  Since the Coronavirus shortages began we've been using it to keep extra meat frozen.  It works well and the temp is usually between 0? - 8?.  It works well as long as I keep the motorhome plugged to the house.  When I run the generator, I unplug the electric and turn on the AC.  This last time I forgot to plug it back in.  Long story short, we lost all the meat in the freezer.  Probably worth at least one 12 Volt AGM. 

Replacing the converter is optional, all that a lithium converter does is raise the working voltage from 13.5 volts to 14.6 volts.  At 13.5 volts a lithium battery will fill to 80% or more, if your converter or solar shifts to Boost or Equalizing charge around 14.6 volts this should top off the remaining 20%.  There's also no harm at leaving a lithium battery at 80% charge, in fact this will increase it's already long life.

I believe ours is a 3 stage WFCO and for what it's worth, our Victron battery monitor has indicated a charge in the 14+ Volt area from time to time. 

garyb1st said:

In order to boon dock more and rely less on our generators we need more than the 230 Ah we get from our 2 Interstate GC2 batteries.

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Just to set the stage, more batteries doesn't mean less generator time.  What goes out must go back in so even if you had a bank of eight batteries, you have to run the generator long enough to replenish whatever energy you use.  You're running the generator either way - with a small battery bank you run off the generator directly, if it's a large bank you run the generator to fill it back up later, but either way you're running the generator.

Second Gary_RV_Wizard's comment about how many Ah you actually need.  Something to look at is you can gain a slight amount of Ah in the same space by using higher capacity batteries.  Trojan T125's are the same physical size as GC-2's.  If you have the vertical space, T145's offer a little bit more.  No tray modifications required.

Mark B.
Albuquerque, NM

If you use AGM lead acid batteries, there is no ventilation requirement.  Ditto for LiFePO4 batteries.

A sturdy wood battery platform/box works as well as metal. Sometimes better, since it is inherently corrosion-resistant and won't short out a stray cable.

You might also consider Firefly Oasis carbon foam AGM batteries, as an in between step, I have not priced them lately so don't know how they are doing vs lithium at the moment.  They give a deeper discharge advantage vs standard lead acid, but otherwise have similar limitations.  When I last looked at them a couple of years ago, the pricing was between traditional lead acid, and lithium.

I see their claims but I'm skeptocal that the Firefly is notably superior to any other decent quality AGM.  AGMs in general have superior resistance to sulfation, a greater number of discharge cycles and other advantages vs a flooded cell lead acid, but the basic lead acid chemistry is what it is.  All the AGM makers brag about their method of wrapping the plates in the glass mat, but there isn't that much difference among them.

garyb1st said:

I'm pretty sure I could build a secure wood platform.  Is there a downside to using wood with lead acid batteries?  If so, I would go with AGM's which would also give me more options. 

Haven't thought about venting.  Guess that's only a problem with lead acid batteries.

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No problem with wood - Most boat banks are built on a wood platform - Don't overbuild but make sure they stay secure in a wreck.  1/2 or 5/8 plywood base. We separated the batteries with 1 X 2 strips - you can hog out the middle of the lengthwise strips (think doorahndle) and use web straps threaded through for tie downs.

I'd vent any compartment used for batteries...

Thanks for all the suggestions.  I've narrowed it down to either building a platform in the bay closest to the converter or buying two lithium batteries and using the existing bay.  If I go with the lithium, I'll just replace the existing lead acid batteries and call it a day.  Aside from cost this is the easiest replacement.  It also will give me more usable Ahs than the two 6Volt EGC2 batteries which are rated at 230 Ah's each. 

The alternative would be a wooden bay with either 3 or 4 12Volt AGM batteries.  The only consideration would be weight.  But at the end of the day, if weight is not a problem, it would be nice to have 4 AGM's with 400 Ahs. 

garyb1st said:

buying two lithium batteries and using the existing bay.
It also will give me more usable Ahs than the two 6Volt EGC2 batteries

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Two group 31 Lithium is 200Ah, basically the same as two GC-2's.  Lithium gets you greater cycle life and lighter weight, but the same nominal Ah in the existing space.

Mark B.
Albuquerque, NM

Mark, you are correct.  My two Interstate CG2's are rated at 230 Ah's.  So greater than two 100 Ah Lithium batteries.  But my understanding is that I get considerably more usable hours from 2 Lithium batteries compared to the Interstates.  If I'm missing something hopefully someone will chime in. 

My understanding is 200 Ah's of Lithium can be safely discharged to 80%.  That gives me 160 usable hours.  Two Interstates at 230 Ah's safely discharged to 50% will give me about 115 usable hours.  A third Interstate would add another 57.5 hours so maybe 172.5 hours compared to 160 from the Lithium.   

Even if discharging the Lithium batteries to 80% shortens their life, for our purposes, it's not really a consideration. 

garyb1st said:

I get considerably more usable hours from 2 Lithium batteries compared to the Interstates

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It depends on how you're using them to some extent.  Lithiums are more efficient at higher draw rates.  At rates increasing towards 20C then that difference becomes less and less pronounced.

Two Interstates at 230 Ah's safely discharged to 50% will give me about 115 usable hours.

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Why stop at 50%?  Wait, don't tell me - because they'll be "damaged" -?  Why are they spec'd to 80% DOD then? 

There are more moving parts to selecting a battery than just Ah, or cycles, or cost.  The more accurately you define your usage requirement the more confidence you will have in your solution.  The debate here isn't whether lithium would work here or not, they will.  It comes down to cost efficiency and if you'll ever own and operate them long enough to recoup the expense of the batteries and the system modifications to accommodate them.  If lead acid can't meet the operational need then your answer is clear, but it'd be worth a couple thousand to me to know that for sure. 

Mark B.
Albuquerque, NM

Anyone have any info on Mighty Max Lithium.  Aside from their advertised 2000 cycles which seems low the price is very good.  Check this out.  https://www.amazon.com/Mighty-Max-Battery-Replacement-ES200-12/dp/B07YP1DTXZ#HLCXComparisonWidget_feature_div

Sold and shipped directly by Mighty Max and at $1,099.85 for a 200 AH battery it's almost too good to be true.  Even if it's only 2000 cycles, for me, at a young 77, that's probably more than I'll need. 

Mark, in answer to your comment regarding discharging lead acid batteries by 80%, I've read that voltage drops the lower the discharge.  This can't be good for anything with a motor or electronics.  Am I misunderstanding something? 

garyb1st said:

$1,099.85 for a 200 AH battery it's almost too good to be true. 

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I didn't look real hard but didn't see a data sheet at the amazon page.  And in general, even with "mainstream" product like battleborn finding detailed performance data is hard to come by.  I think that's because the secret recipe for these things is still in flux and no one will sign up to any hard numbers.  Odds are they work "well enough" so that they don't come back under warranty, after that you're on your own.  Few will ever exercise these things to the extent that proves they failed specification.  Especially if they live long enough to trade hands, after that all history is lost.  In my view with any battery you're buying it for what it can do for you today, not some ideal use case that makes you think you'll still be using it 10 years or more from now.  That's way beyond the ownership span of most anything these days and any equity after a few years in my view is long gone.  Look at electric cars and hybrids.  Even with a "known good" battery of a given age or miles the residual value of these things isn't great.  Consider what a failure looks like, either through defect or misuse.  You're out a $1K plus battery that may have only served you as well as a $200 one.  So there's a bit of risk exposure there for sure.

I've read that voltage drops the lower the discharge.

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All batteries do to some extent or another.

This can't be good for anything with a motor or electronics.  Am I misunderstanding something?

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That's very device specific.  Anything spec'd for an automotive environment will easily operate over the entire voltage range of a lead acid battery.  Consumer goods may not be, as they may have been designed to work with a power supply or power adapter of a bit lesser range.  Motors are a tough one, whether they're direct connected or operated through a PWM controller and what the end torque requirements are.  Ideally the motor would be conservatively spec'd but that costs money, so there may be practical limitations there.  This isn't a heart-lung machine or a space craft,  it's a water pump (or whatever) in an RV,  Some mis-operation may be expected to be tolerated.

I consider operating voltage range a "system level" issue.  The operating parameters of any given battery are well documented and understood.  Electrical and electronic devices the same, either through design or characterization.  In my view, it is incumbent upon the system designer, in this case the RV manufacturer to ensure that the components they've selected (batteries, lights, electronics, motors, controllers) are all compatible with each other over all their expected uses.  Since with any RV built with lead acid batteries it would seem reasonable to assume that all of the devices would operate correctly over the entire specified voltage range of the battery.  It's not a stretch to say that may not always be the case.  So if you're lightly cycling your battery to accommodate equipment that isn't specified or capable of operating over that battery's voltage range that's not a battery problem, it's a component problem created during system design for any one of a number of reasons.  So that kicks the problem down to the end user that will need to accommodate that shortcoming.  Nothing new in the RV world, unfortunately.  So you get to decide between working around it or re-engineering the affected subsystem.  In the grand scheme, never letting the voltage go below a given operating threshold to compensate for limited range devices is a simple first-order solution and if you're OK with that then fine, but the real answer is to spec and build the system to work correctly under all boundary conditions.  Something tells me economics are the primary driving force here, where it's easier to install smaller gauge wire and less capable devices and let the user work through the problems.  If you want to solve that by throwing a $1000 battery at it then more power to you (pun intended) but I believe you'll be heading into a different range of uncharted waters with that. 

In reading the forums here the greatest endorsers of lithium are usually full timers.  Folks that ride batteries hard and put them away wet.  In that case I can easily see how a battery spec'd for thousands of cycles and excellent capacity would be a game changer.  It'd be easy enough to say these would work well for everyone and in the grand scheme I'm sure they would work fine in almost all applications.  But that's not taking into account acquisition and opportunity costs which a lot of people may care about.  Which is why lithium hasn't totally supplanted lead acid yet - there are use cases out there (myself included) where lead acid is still a cost effective storage solution. 

Mark B.
Albuquerque, NM