Views: 0 Author: Site Editor Publish Time: 2026-02-23 Origin: Site
If you work with lithium pouch cells long enough, you’ll notice a pattern.
Most buyers start with the same approach:
They send a BOM.
They match voltage.
They increase capacity.
They copy the original pack design.
On paper, everything looks correct.
Three months later, the emails start:
“Battery swelling.”
“Runtime shorter than expected.”
“Device won’t power on.”
“Our customer is unhappy.”
We’ve seen this play out many times — especially with replacement battery projects and custom pouch cell packs.
The problem is simple:
Pouch cell selection isn’t about copying parameters. It’s about understanding how those parameters interact in real applications.
Here are the five most common mistakes we see in lithium pouch cell sourcing — and what experienced buyers do differently.
One of the biggest advantages of pouch cells is flexibility in shape.
It’s also their biggest trap.
Unlike cylindrical cells (18650, 21700) with standardized dimensions, every pouch cell is effectively custom. A difference of 1–2 mm in thickness or tab position can stop assembly entirely.
We once supported a medical device project where:
Cell body size matched perfectly
Capacity matched
Voltage matched
But the tab spacing was off by 2 mm.
The customer’s plastic housing had fixed terminal posts. Bending the tabs caused insulation damage near the root. That batch had to be reworked.
Freight loss came out of our pocket.
Not just length × width × thickness.
You should always confirm:
Cell body dimensions (including gas pocket area)
Tab material (aluminum / nickel / nickel-plated copper)
Tab spacing (±0.5 mm matters)
Tab length
Top seal width
For pouch cells, drawings matter more than datasheets.
Higher capacity sells easily.
But pouch cell chemistry is always a compromise between:
Energy density
Power capability
High-capacity pouch cells use thicker electrodes. That increases internal resistance.
If your application involves:
Motors
Vacuum systems
UAV propulsion
Robotics
then current draw matters more than headline mAh.
We often see buyers replace two parallel cells with one large single pouch cell because capacity “looks equivalent.”
What gets missed:
Parallel cells share current.
Single large cells must carry it alone.
Result:
Voltage sag.
Unexpected shutdowns.
Heat buildup.
Accelerated aging.
Before selecting capacity, confirm:
Continuous operating current
Peak current and duration
Duty cycle (continuous vs intermittent)
Let the supplier recommend a pouch cell formulation based on load profile — not just capacity.
Every lithium pouch cell expands during cycling.
That’s normal.
What matters is how much.
Swelling depends on:
Cathode chemistry (high-nickel NMC expands more than LFP)
Formation quality
Residual moisture
Charging behavior
Thermal conditions
Hard-shell cells hide this.
Pouch cells show it immediately.
We’ve seen packs fail simply because enclosure designs left zero expansion margin.
Once swelling starts pressing against rigid housings:
BMS boards crack
Enclosures deform
Electrical connections loosen
Specify max cycle swelling (typically ≤10%)
Leave thickness margin in pack design
Use foam or light compression structures for high-rate systems
Mechanical allowance is part of electrical design.
Pouch cells don’t include protection circuits.
Everything depends on the BMS.
Here’s where many replacement battery projects fail quietly.
Different pouch cells may share nominal voltage (3.7V), but have different charge cutoffs:
4.20V
4.35V
sometimes higher
If you charge a 4.35V pouch cell with a 4.20V BMS:
You never reach rated capacity.
Reverse it:
Overcharge risk.
Another overlooked issue: tab metallurgy.
Positive tabs are aluminum.
Negative tabs may be nickel or copper-based.
Wrong welding process = weak joints.
We see failures caused not by chemistry — but by mismatched welding methods between BMS and pouch tabs.
Charge cutoff voltage
Discharge cutoff voltage
Tab material compatibility
Welding process (laser / ultrasonic / resistance)
BMS must match the pouch cell — not the other way around.
Pouch cells ship at partial SOC for safety.
But pouch cells also have slightly higher self-discharge than cylindrical cells.
If stored too long without voltage checks:
Cells can drop below 2.5V.
At that point, copper dissolution begins internally. The damage is permanent.
Transportation introduces another risk: tab puncture.
Without proper separators, vibration can allow exposed tabs to pierce neighboring pouch envelopes.
That’s how internal shorts start.
Monitor storage voltage regularly
Recharge if below 3.0V
Control warehouse humidity
Use layered packaging to isolate tabs
Logistics is part of battery quality.
Lithium pouch cells are excellent when properly applied.
They offer:
Higher energy density
Flexible geometry
Lightweight design
But they are less forgiving than cylindrical or prismatic cells.
In B2B projects, most failures don’t come from bad chemistry.
They come from:
dimensional assumptions
mismatched discharge profiles
overlooked swelling
BMS incompatibility
storage shortcuts
As a pouch cell supplier, our role isn’t just to ship cells.
It’s to help customers avoid these mistakes before production starts.
If you’re currently evaluating a pouch cell battery project — especially replacement packs or custom assemblies — feel free to reach out.
Some problems cost months to fix.
Others only require asking the right questions early.
