The 40T might be slightly less expensive?
Otherwise the P42A is my slightly better choice for those two.
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thanks Mooch, mooch appreciated =D
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40t is almost 2cm shorter in a 12s4p pack. For a hummie deck that means almost no extra routing for example.
Also, wasnāt p42 cheaper?
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Yeah, P42 is cheaper, though i think iāve seen prices fluctautate. I seem to remember 40T being cheaper (on fogstar) at some point, but now itās more expensiveā¦could be imagining this though. But yes, in a hummie 40T requires little, if any routing im led to believe.
It was cheaper but molicel really, really wants to undercut samsung on this one for some reason
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At lower current draw the T40 have more capacity making them better in larger packs
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Arenāt they both ~4100mAh in ideal conditions?
At different currents batteryās have different capacity
T30 punch hard to begin with then p42A very quickly keeps a higher voltage
T40 good at low currents
P42A come out as a better all rounder by quite a big margin
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Yes, iām talking discharge at something like 100mA
P42A sag a lot at the start giving the T40 the edge on capacity but thereās very little in it after that.
Personally Iād go with P42A more consistent acros there range the capacity bonus is so minisqal itās not worth it
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How are the packs shorter? Arenāt they both of standard 21700 size? Also @Geo_Engineering_FTW might have an answer.
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P42aās are 21.7mm wide, in which the extra .5mmish adds up when you get 24 of them lined up.
I ran into this issue designing a p42a pack.
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P42a is 21.7mm wrapped. That times 24 is 16.8mm more, or simply put 2cm longer
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they are shorter as @Athrx says. for my hummie i could have fitted it all in without routing any extra space, but it is super tight, so i decided to route about 8mm at one end to make cable management easier
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Show me how yours is doing so far lol
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heh, will do. am painting it at the mo 
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I do it often
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@Battery_Mooch I got some questions for you Iāve been wanting to ask you:
What would be the best way to meassure cell aging considering they are still assembled in a 12s4p pack. I understand Iāll need to measure IR, but whatās an acceptable range?
What would be the main cause of cell drifting? I know they tend to drift when p-group connections are poor and have high resistance, when the BMS goes bad or when you use a high current charger
I understand
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DC and AC IR donāt change much over the life a cell until itās really worn out. IR is also state-of-charge and temperature dependent, making consistent testing tougher.
AC IR values are quite low, so differences are hard to see, but the test results are barely affected by lead and connection resistances. DC IR is higher, and easier to test, but the results are affected more by the resistance of the leads and connections. This isnāt an issue though if the resistance of the pack or cell is measured when new and changes to the resistance are measured over time.
The big manufacturers typically donāt spec IR change for determining end-of-life but, IIRC, I have seen a 15% increase mentioned. That is tiny and tough to measure.
Capacity loss over time can be easily measured though if a good tester is used. Most chargers that test capacity are very inaccurate but could be used if they are very consistent. Of the ones I have tested the SkyRC MC-3000 was pretty good for capacity checking and good for DC IR checking if you pressed against the bottom chargers contact while measuring.
You would also need to decide when a cell has reached āend of lifeā. That is, how much of a capacity or IR change do you accept before replacing the cell(s)? Most manufacturers spec cycle life out to a point where the capacity has dropped 20%. Though I have seen a couple cells specād out with a 40% loss before the cell is said to have reached end of life.
Most cells can be used far beyond this point but any damage to the cells is accumulating at the same time and that, without any data to help you decide, must be taken into account. This is why a conservative number like 20% loss is often used.
Differences in self-discharge rates will cause cell (or p-group) voltages to drift apart in series strings without a BMS. With a BMS they should all be the same voltage once balancing is done. But immediately after that they can start drifting again. This typically isnāt an issue unless the pack is being stored for a while.
Cells within p-groups will, of course, balance themselves out but that can take a bit of time if the charge rate was very high and/or the connections within the p-group are bad. Each p-group can settle at a different voltage though.
Higher charge and discharge rates accentuate the IR differences between p-groups and cells and will create temporary voltage differences, within and between the p-groups. These differences disappear once the current flow stops and the p-groups balance themselves internally. Voltage differences due to differing capacities between the p-groups however do not disappear when the current stops. The BMS must fix these but if the cells were top-balanced before then when they are recharged they should all end up balanced again without BMS intervention.
As mentioned earlier, the BMS must also compensate for the different self-discharge rates of each p-group too. Though that typically isnāt much of a concern unless the pack is being stored for a while.
If there is no BMS then balance charging needs to be done occasionally. There are no guidelines for how often. The p-group voltages will need to tested over time and a schedule determined from that. There are no guidelines for determining how much of a difference in p-group voltages is acceptable. It depends on how hard they are being used, what the low voltage cutoffs are, etc.
The bigger the differences though, the worse the pack performance will be. Safety, solely due to p-group voltage differences, shouldnāt be an issue as long as none of the cells ever drops below 2.5V. This is ignoring any safety issues due to internal cell damage, temperature abuse, over/under-discharge and charge, and any other misuse or mishandling.
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Anecdotal evidence does not offer proof, but I also use chargers in parallel occasionally and havenāt had any issues.