What are your thoughts on the topic @Battery_Mooch?
Interesting subject indeed.
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That is the whole thing : there is no rebalance nor sag! The cells are parallel, one can’t be lower in voltage than another one.
Just imagine it like super slow mo in your head, like how would current go it’ll make sense 
I love that we are having technical debates here, this truly makes this community what it is
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I look at the energy balance for the cells, a P42A has 14.4Wh and a 50E has 18Wh so the cells have to drain at a rate proportional to the energy they have left, which means the 50E MUST supply more energy, either it is the form of current which will damage the cell or in the form of heat, which will still damage the cell
Based on the current the cells should be draining at the 50E should have around 3Wh to maintain good chemical reaction rates, so you are loosing more energy than a P42A for each 50E cell assuming a 1:1 ratio of cells in the parallel group
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Oh for sure, where would the fun be if couldn’t discuss things
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Very good point actually, this is true it would be an issue if the load was above maximum cell output current throughout the whole discharge then the 50e would have to empty itself faster.
But to be honest this is practically never happening, and their is no absolute maximum current for a cell. It’s only a matter of heat. Moreover, it will never pull that much juice. And for small differences ( p42a and 50e or 30Q a’d 35E ) it’s safe.
Yeah a 4:4 split P42A and 50E pack is fine for anything under 71A in theory, the numbers depend based on the actual functional rating of the cell but once you start pushing above that limit you can get into cell degradation territory. But at that point you might as well have just an 8p 50E and get all 78A and the extra few Ah of capacity
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Nah mate this is not proper maths haha
Just like if you put several 10s packs in parallel, even if those are different, it won’t be a problem as long as you add up capacities and current capabilities
So you’d run a 3s lipo and a 7s watch battery in parallel then pull 100A from it? They come to about the same voltage
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I’ve got 50e and no sag
That’s a dumb ass argument
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Running some simulations, easier to show what happens that way. 
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At the start of a discharge the capacity and nominal energy in each cell has no effect on the amount of current each cell will supply when paralleled. The internal resistance of the cell and the resistance of the connections between the cells and other connections determine how the current is shared.
Once the discharge has proceeded for a while though then the lower capacity cells will eventually try to drop their voltage faster than the higher capacity cells. The higher capacity cell will compensate by pumping out more current. At a certain point the lower capacity cell needing this compensation more and more will wipe out any benefits from its lower internal resistance and the higher capacity cell will start delivering more current than the lower capacity cell. Whether this happens during normal use for the application in question depends on the cell capacities, internal resistances, discharge current level, and low voltage cutoff point.
I’m running some simulations to better show what happens and will post to a new thread.
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One cell can’t drop faster than another one, these are in parallel and are constraint to have the same voltage.
Just imagine that you have only the p42a cells in the p group, the pack would work solely with the added specs of the p42a cells. Simple.
Then you add a few 50E cells in parallel so that they will ‘’ recharge ‘’ the p42a while these still do the job. So you keep the previous discharge rate for now and add the capacity of the 50E.
Still okay?
Now as for current, the 50E that ‘’ charges ‘’ the p42a can be considered like added current at the same place of the p42a discharge current.
And this current maximum is the discharge current of the 50E.
Still pretty basic.
The tricky part is that the greater capacity of the 50E means that, in case of maximum cell current during the whole discharge, the 50E should drain faster than the p42a to meet emptiness both at the same time.
But fortunately, with such powerful cells this is never happens for more than a few minutes max.
So for our application you can just combine the specs of the added cells.
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Thanks for your time. I understand the setup we’re discussing but I was in a rush and could have worded my post better (as I did in my other post).
The lower capacity cell will try to drop its voltage faster and the higher capacity cell will then provide more current to compensate. The voltages will stay the same since, as you mentioned, they are in parallel.
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Have a look here
https://secondlifestorage.com/index.php think i is down at the moment.
They have a repacker calculator for mixed cells
But internal resistance plays a big part stay with under 40 ohms, and try to average cells
Look for repacker, it’s a calculator
Couldn’t cells be mixed if you specced the current output to be as if you built the entire pack out of the highest resistance cell in the mix?
The internal resistance is important for current sharing but the capacity is important for run time. The lower capacity cells will eventually end up drawing more current from the higher capacity cells, reducing the run time for the pack.
So would a high voltage cutoff work? Either way this seems very impractical
A few thoughts and some simulations of what happens if you mix cells: Here’s what can happen when you parallel (mix) different batteries in a pack
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