Additional LiFePo4 batteries

[RoamingKat]

I currently have 12v 400ah lithium.

I am seeing places where I can buy additional cells (aluminum clad because they are smaller, lighter, and conduct heat faster) 

So... I am trying to envision how to connect them.    The second 400 cannot be even close to the first ones.    So, if I have two totally separate banks, the question becomes switching between them.    
I don’t think I will need to be able to push 600 amps at the same time, but would like to be able to let one bank rest for a couple days and operate off the other meanwhile.     Someday, when I get the earthship home I want to build; I will create one 800 amp battery with all of them.  (After checking capacity for the old ones). 

So...with 2 solar charge controllers, I think I can figure out a switch to change from one to the other.
I wonder if I can use a single master switch for both charge and discharge.   

The battery monitor would need to be worked out.    Currently I have a victron monitor that is grounded to the shunt and positive directly onto the battery terminal.    What happens if that battery is turned off on the master switch?   Will that monitor continue to read “true”?    Won’t it still “see” the power thru the shunt even though that battery isn’t providing that power?    I don’t mind having two separate monitors

I will have to figure out a way to switch the temperature control too.    Right now the temperature monitor is wired to two contactors,    One to ring an alarm and turn on the compartment heat when the temp gets down to 36....the other rings an alarm and turns on the compartment fans when the temps get to 95.      Having a second temp probe wired to the same contactors is probably too confusing to sort out.

Balancers are simple enough.  Everything else already runs through a master switch... I think I can trade it out for a marine switch that uses 1, 2, both, off.   

Any ideas on what I should be thinking through?   Anyone know a reason this won’t work for me?

[Roadtripp]

Ok, I’m a bit confused but that’s not unusual lol. Why not simply make a duplicate of the 400 a-h you have now and place it in parallel with the existing battery. 
 The Victron meter will not count a-h accurately for two separate battery banks. It will measure current and voltage separately.

[Roadtripp]

This company makes DC transfer switches. I imagine they are costly:
https://lake-shore-electric.com/product/...-switches/

A “Changeover Switch” might be what your looking for. This one is inexpensive but I not sure it s rated for enough amperage:
https://www.amazon.com/VictorsHome-Changeover-Positions-Terminals-Universal/dp/B07N11925K/ref=asc_df_B07N11925K/?tag=hyprod-20&linkCode=df0&hvadid=317966907488&hvpos=1o13&hvnetw=g&hvrand=660114259067396516&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=1027669&hvtargid=aud-801381245258:pla-677576302516&psc=1xe

This changeover switch has a 125 amp rating but costs more:
https://www.amazon.com/Baomain-Rotary-Changeover-LW28-125-Position/dp/B01E8IMZV6/ref=sr_1_13?keywords=Changeover+switch&qid=1576516444&sr=8-13

[RoamingKat]

Ok, I’m a bit confused but that’s not unusual lol. Why not simply make a duplicate of the 400 a-h you have now and place it in parallel with the existing battery. 
 The Victron meter will not count a-h accurately for two separate battery banks. It will measure current and voltage separately.

Distance.   The longer the distance the greater the electrical resistance.     With batteries in parallel they need to be very close to each other....not the 3-4 feet I will require.      At 3/0 I could handle 220 amps...probably go 4/0 to be safer.....but that still will cost in resistance.   Plus, I do not need to get anywhere near that close to amps in use...so why go through all that?

I looked at the 400 amp transfer switch....wow is that huge....cannot afford that much space

[Roadtripp]

Try the third link. That’s the 125 amp changeover switch and it’s only $40.

[RoamingKat]

Try the third link. That’s the 125 amp changeover switch and it’s only $40.

My max draw (so far) is my A/C unit.   It pulls up to 200 amps when the compressor is full on.

hummmm.....might not be so easy to find 250 amp?  Switch that isn’t more space than I have.  
I’ll go looking at the marine supply houses.    

still, what does this idea look like?   Think it is doable, safe, did I forget something?

[RoamingKat]

Found this....looks like just the thing....

https://www.westmarine.com/buy/perko--me...cordNum=12

Does up to 250 amps.

So, back to all the other questions.

[Roadtripp]

As Lithium batteries have lower internal resistance than lead acid batteries I’d be hesitant to connect a discharged pack to a charged pack directly with a battery switch like the . I’m not sure how high the current flow would get?? 
Is your idea to have one pack charging but disconnected from the loads while the other one supplies the loads?? Ive thought about that strategy of rotating battery packs. One could be on a cart that is wheeled around camp or worksite. There’s lots of possibilities. 
  This brings up the idea to connect packs with a DC to DC charger. Or a RC charger discharger. Ive been wanting a icharger 4010 duo for a while to play around with Lithium packs. 
 The resistance of 3-4 feet in 4/0 cable is negligible. Even at high amperage and low voltage. Over 6 feet it becomes more of a issue. But balancing the cables is important. Especially with lead acid or lithium without any balancing circuit. With active balancing on Lithium packs balancing the cables might not be so important. 
 I’m no engineer but what you have in mind might work.

[sternwake]

My first 1/2/both/off switch was a Perko. slightly different than the one linked. It eventually became highly resistive, the contacts likely wearing out from lots of switching under load over a decade, and I replaced it with physically smaller Blue seas 6007m models that have higher amperage ratings.

My new BS switches don't have alternator field disconnect, my Perko did, but I did not employ it.

Be aware that switching to OFF with engine running can grenade the alternator's diodes, when the AFD is not employed.

There are switches that are make before break, and those that break connection beforethen making the new, though the latter are more rare.

[Blacktank]

Found this....looks like just the thing....

https://www.westmarine.com/buy/perko--me...cordNum=12

Does up to 250 amps.

So, back to all the other questions.

https://www.amazon.com/Blue-Sea-Systems-Selector-Battery/dp/B000MMFJH0/ref=asc_df_B000MMFJH0/?tag=hyprod-20&linkCode=df0&hvadid=312114712708&hvpos=1o12&hvnetw=g&hvrand=1479530842581513380&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032901&hvtargid=pla-434093571586&psc=1