(I complained about a withdrawn post, I have no argument with racemaster)
Let me describe how it will actually work with 2 different-sized parallel battery packs. This is unfortunately very long, because I'm going to be VERY detailed in this response.
The 2 battery packs are attached on a parallel bus. The current draw will generally favor the less resistive battery pack (that resistance includes both the cells, AND the BMS resistance during 'discharge' operation). This may tend to pull on both battery packs equally, as you describe - and it may even tend to pull somewhat more from the "smaller" battery pack. In that latter situation, it might be good to use longer lead wires from the Busses (grounding and positive) to the smaller battery terminals, making it somewhat less attractive. That could prevent over-current with the less capable battery pack.
But when the "150Ah" battery pack becomes significantly discharged, its internal voltage in discharge state will begin to fall off from a nominal 2.8V value. The less discharged bigger battery will not yet have that voltage roll-off, and it will become a more attractive source for providing the load current. It's changing "attractiveness" will vary, according to the different SOC and discharge Voltage of the two battery packs.
In real life, neither battery pack should be driven into that low SOC on a frequent basis. But when it occurs, the imbalance of SOC between the two packs will be largely self-correcting, with the bigger pack being PULLED DOWN towards the SOC of the smaller pack.
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There can be a similar discrepancy in
charging unbalanced packs, until one of the packs reaches a high SOC and Voltage begins to increase significantly. At first, the larger pack (now accepting a bit more charge current, with a lower internal Voltage) is only slightly more attractive. But, as you approach and then reach balancing voltage on the smaller pack, its BMS will switch to balancing mode, and only accept very small "balancing current". ALL of the remaining charger current will be available to the larger and less charged battery pack. This situation is also self-correcting, with just one limitation: The BMS within the "larger" of two packs, or the "largest" of 3 packs, must be able to accept the full current of the charger.
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As Elicon123 describe within the preceding post, this kind of configuration is NOT otherwise a problem in real life. In discharge, some small "tuning" changes to the resistance of the terminal connection wires might be desirable, If I ever do that to my own batteries, I will simply lengthen the wires from the "grounding bus" to the individual terminals of the smaller battery packs.
Up to this date, in my own small RV configuration (with slightly dissimilar battery packs in parallel), no such "tuning" has been necessary. But, if I add a 3rd pack with MUCH larger capacity than the others, and then try to run the Air Conditioner from batteries exclusively, a significant reconfiguration may be helpful. (I would probably want to lengthen grounding wires on the two "small" battery packs, causing more current to be drawn from the "big" battery pack).