Why would it impact voltage reading if they were connected in parallel? a 12s2p and a 12s1p in parallel connection will have the same voltage reading no matter what. Unless diodes were put in place for some strange reason.
Well at least there’s a discussion 
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Legit information, you can put any packs in parallel as long as the S matches and chemistry is the same. Brand new 12s100p will parallel with well used 12s1p. The criteria is: match voltage, disregard capacity. As long as full charge on both battery is identical in voltage, you can keep slapping parallels together all day long. Anyone with EE knowledge can back this up.
The tricky part is all “independent” packs need a BMS. so either both packs have balance leads hooked together, or they use their own individual BMS with parallel power leads.
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That was my plan.
Soooo I don’t know what to do as there is multiple takes on my case.
I suppose I’ll accept my crappy range and buy a proper battery in due time.
If both packs have their own BMS, go ahead and parallel them all you want. Just connect them both when they are at the same voltage. You will essentially have a 12s3p. No offense to anyone but anyone who thinks you cannot parallel same series count packs needs to read up on fundamentals of electricity again.
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Is there a margin or do you mean “exact same” ?
I’m gonna say within 0.5v max. Its a simple ohms law calculation, I = V/R. The more resistance between the pack, the more voltage difference is acceptable to keep initial current down. On an approximation, within 0.1v is negligible, up till 0.5v will be nothing the packs can’t handle. Easy way is to fully charge both. It’ll be almost identical that way.
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Mmm ok then, thanks mate
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The only thing I would add is keep the BMS the same or at least same specs. It does not affect charging really but in discharge, if one BMS cuts low voltage way before the other, you’re down to 1 pack running. If cutoff voltage is similar, or you’re running bypass, you’re all clear.
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I would agree with @BluPenguin. you can connect as many batteries in parallel as you want, if they are same S count. You can use them without bms, but best and safest would be if each battery has its own bms (to protect overcharging/overdischarging - for example if you connect batteries in parallel when one is at 42v and another on lets say 36v - bms should here protect 36v battery from immediate balancing with 42v battery)
only reason why not connecting separate batteries in parallel is actually available space - you need more space for another bms, wires, battery wrap and insulation and so on.
If you do connect a 12s1p that could only draw 10amps for example, to a 12s100p in parallel. If you draw 100 amps, the 1p pack will be fine?
Correct, in parallel, you add their discharge capacity together, and any draw is averaged out to all cells. Electricity is not selective, it won’t “only” discharge from the smaller pack. the 12s100p will see 99% of the power load and the 1p will see 1% (based on capacity)
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And in return, will there be any problem when batteries are discharging?
Will voltage decrease evenly in each battery? If not that would make them impossible to charge
(Sorry as you noticed, this is all very new to me)
You just got me thinking:
One could thoretically make a battery pack with mixed cells as long as each p-group has the same ratio! For example:
A 12s4P battery made 50% out of Samsung 40T cells, and the other half of 30T cells (4Ah 30A discharge and 3Ah 35A discharge respectively). This would give you a 14Ah 130A pack in the end 
So by mixing and matching, you can fine-tune the pack to your exact needs 
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Voltage drop on one battery could cause issues. I have a DC to DC constant current voltage booster for this kind of stuff
They will discharge evenly, because as soon as one pack is a bit above the other in voltage, it would charge that pack until they are balanced again. Basically the same thing that happens in p-groups, but on the scale of a whole pack.
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Damn guys two opposite answers, what would I believe??? 
I think @Fosterqc is talking about an external second battery to charge / use alongside your main battery, where since it is not permanently connected, you could end up with different voltages, which would be problematic. In your case, you want to add it permanently to your existing setup, so there shouldn’t be a problem if you do it when both are fully charged (or just at the same voltage when you connect them).
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OK then
Anyway it looks like it’s not easy to find a 12s1p
Thanks again everyone who helped
Well since you can use any cells, you could just make one. Shame there aren’t any 1s1p NESE modules to make it easy for you 
@Agniusm
Edit: actually, it would make a ton of sense to have a NESE module where the cells are all in a row, connected in series, and you have a ton of external small connectors for the balance wires. Building large packs could be a hassle, but if there was a single piece 10s3p, or 10s4p, 10sWhatever-p module, it would be very easy
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