Hi guys.

I am in the process of replacing all my Pylontech BMS boards with JK ... Pylontech passive BMS simply does not cut it and recently Pylontech is cutting corners when comming to warranty cases..

Anyway, short story .. I have 10 x Pylontech US3000C running in parallel with 1 x 105Ah JK BMS battery built with 15x105Ah Eve cells , so same voltage. (need to test before I change all BMS inside the Pylontech boxes).
All batteries are connected to same buss bar , using same length cables.

Looking at the current draw , I see at a stable load , the Pylontech are discharging with 100-115W and the JK (even being an 100Ah battery) is only pulling 67-70W.

Why is that ?

Edited October 23, 2025Oct 23 by Jaxone

10 minutes ago, Jaxone said:

Hi guys.

I am in the process of replacing all my Pylontech BMS boards with JK ... Pylontech passive BMS simply does not cut it and recently Pylontech is cutting corners when comming to warranty cases..

Anyway, short story .. I have 10 x Pylontech US3000C running in parallel with 1 x 105Ah JK BMS battery built with 15x105Ah Eve cells , so same voltage. (need to test before I change all BMS inside the Pylontech boxes).
All batteries are connected to same buss bar , using same length cables.

Looking at the current draw , I see at a stable load , the Pylontech are discharging with 100-115W and the JK (even being an 100Ah battery) is only pulling 67-70W.

Why is that ?

Shot in the dark. What is the resistance across the jk bms vs the pylon ? Maybe one of them just not reporting correctly ?

That I did not test , but both use SAME type cable , same length , connected to same bus bar... will do some measurements in the weekend and change internal JK BMS power cables as they seem to be pretty flimsy.

This might shed some light on your situation.

@TaliaB I am not complaining about SOC , I am "complaining" about current draw from the batteries.
The Pylontech are all US3000C 74AH , the JK BMS has 105Ah with Eve cells. Maybe EVE cells are not quite grade A or something like that ?
Each Pylontech draws around 75-85W (1.7-2A ) and the JK draws 60-65W (1.3-1.4A) and they are all in prallel.

@Stefan Cornelissen Meassured JK across 0,1 ohm , same as Pylontech. (When connecting the Fluke leads together I get the same 0.1 ohm).

Edited October 23, 2025Oct 23 by Jaxone

9 hours ago, Jaxone said:

@TaliaB I am not complaining about SOC , I am "complaining" about current draw from the batteries.

Actually, these two (SOC and current) are tightly coupled together, which would be why @TaliaB is pointing this out.

SOC is being calculated via integration of current over a time, therefore:

• If the current measurement is not precise, the SOC will deviate a lot.

• Vice versa: if you see that the battery is reporting incorrect SOC, the most probable root-cause is the current measurement error.

It's important to keep in mind, that the current measurement in BMS is working within a range 0,1A - 200A typically, charging and discharging combined. All of this using the same shunt resistor. For example 200A/100mV shunt has resistance of 0,0005 ohm and at 2A vs 1,4A it will produce 0,001V vs 0,0007V. This goes to the amplifier then to ADC. Therefore, it's basically impossible to measure small currents precisely, no matter how hard you calibrate. Lower the current, higher the error.

Back to your issue:

From my point of view, it's just the current measurement error caused by a different shunt type and calibration of JK vs PYL.

In order to check it, just measure and compare current of each battery at a steady load using your Fluke, not BMS.

Edited October 24, 2025Oct 24 by Youda

It's just like different age batteries of even the same manufacturer will have different current draws.

You can't expect the same draw from different manufactures and different construction.

11 hours ago, Jaxone said:

@Stefan Cornelissen Meassured JK across 0,1 ohm , same as Pylontech. (When connecting the Fluke leads together I get the same 0.1 ohm).

Needs to be more accurate than that.

1 hour ago, Jaxone said:

.. I have 10 x Pylontech US3000C running in parallel with 1 x 105Ah JK BMS battery built with 15x105Ah Eve cells , so same voltage. (need to test before I change all BMS inside the Pylontech boxes).
All batteries are connected to same buss bar , using same

Each battery has a slightly different internal resistance, even if they’re the same brand, age, and model. A typical 48 V LiFePO4 battery might have: R₁ = 20 mΩ, R₂ = 22 mΩ R₃ = 19 mΩ When placed in parallel, current divides inversely proportional to resistance:
I1 : I2 : I3 = 1/R1 : 1/R2 : 1/R3 So, the lowest-impedance battery will carry slightly more current.
At small loads (say <10 A per battery), the difference might be <1 A.
At higher loads (e.g. 100 A total), the spread could be 5–10 A or more between units. Even if the batteries are identical, unequal cable lengths, lugs, or terminal tightness can add milliohms of resistance — enough to skew current sharing. For example: 0.5 m of 35 mm² copper = ~0.25 mΩ.
If one cable is 20 cm longer or has an extra crimp, it can make a 2–3 % current difference at 100 A. That’s why busbar symmetry (same-length, same-gauge cables) is critical.
Batteries with slightly different state of charge or voltage calibration (BMS offsets, etc.) can also change current flow: The one with the highest resting voltage tends to discharge more. During charging, the one with lower voltage tends to accept more current (until it catches up). Over time, the BMS balancing compensates for this, but in systems mixing different ages or brands, differences can persist.

Edited October 24, 2025Oct 24 by TaliaB

Thanks everyone for input. Will do some more tests over the weekend and I guess I can "force" more draw from the bigger battery by just shortening the cables.
Anyway , I observed that this behavior is only at very low load shared across the batteries.

If I increase the load at 5-6kw I see the JK will start delivering more that the Pylontechs. I am just getting used to this JK Bms and prismatic cells...
I am thinking I will be adding a 300Ah JK battery next week and dont wanna end up with 80% soc on that while Pylontech is at 10% :)

Thanks for all the inputs and will try to play a bit around and let it run for longer time to see how all works together and possible solutions to the "problems" , if any :)

6 minutes ago, Jaxone said:

Anyway , I observed that this behavior is only at very low load shared across the batteries.

This exactly support current measurement error theory.

Just now, Youda said:

This exactly support current measurement error theory.

I'll re calibrate the JK BMS current and check if it changes anything. Thanks.

1 hour ago, Jaxone said:

I'll re calibrate the JK BMS current and check if it changes anything. Thanks.

You might find at such low levels like 2A you calibrate it just to find at over 50A you are having another mismatch. This happens a lot with the wide range of measurement. The same we can get on power meters when measuring say 5W when the meter is capable of 80x230=18400W.

Update: Problem solved. I have replaced the flimsy wires that came with the battery case that were going from BMS to battery and terminals and from battery to the terminals.
Now the battery works as intended (or as I think it should) and draws same or more power than the 74Ah Pylontechs in any load conditions.

@Scorp007 Not sure I follow what you mean with the 2A ? Usually I calibrate with lab power supply and 10A.

Thanks everyone for the input.

Edited October 24, 2025Oct 24 by Jaxone

24 minutes ago, Jaxone said:

Update: Problem solved. I have replaced the flimsy wires that came with the battery case that were going from BMS to battery and terminals and from battery to the terminals.
Now the battery works as intended (or as I think it should) and draws same or more power than the 74Ah Pylontechs in any load conditions.

@Scorp007 Not sure I follow what you mean with the 2A ? Usually I calibrate with lab power supply and 10A.

Thanks everyone for the input.

I got 2A from this statement placed yesterday. Glad to see you got all sorted out.

the Pylontech are discharging with 100-115W and the JK (even being an 100Ah battery) is only pulling 67-70W

@Scorp007 Ahhh , ok , now I got it :)