Why LiPo Batteries Need Extra Space and Why Swelling Is Dangerous
Lithium Polymer (LiPo) batteries are widely used because they are light and powerful. However, many people ask: Why can’t a LiPo battery be made exactly the same size as the battery case? The answer is safety.
Why LiPo Batteries Cannot Fit Tightly in the Case
LiPo batteries need extra space to “breathe.” During long-term use, a LiPo battery may slightly expand. If the battery is put into a very tight case with no space, it may be pressed by the case, which is very dangerous.
There are four main reasons:
Space for normal expansion
During charging and discharging, a small amount of gas is slowly produced inside the battery. This can cause the battery thickness to increase by about 1–3% over time. Extra space allows this normal aging expansion safely.
Avoid internal damage
If the battery is squeezed, stress points may form inside. This can damage the separator or electrodes and cause an internal short circuit, which may lead to fire or thermal runaway.
Better heat dissipation
A tight case blocks heat from escaping. Heat buildup will speed up battery aging and gas generation, making the situation worse.
Protection from shock and vibration
In case of drops or vibration, the reserved space (usually with soft foam) helps absorb impact and protect the battery.
For safety, engineers usually keep 0.5 mm to 2 mm space on each side, depending on battery size and capacity.
Why LiPo Batteries Slightly Expand During Use
Slight expansion is a normal aging process and happens slowly. It mainly comes from two chemical reasons:
SEI layer changes
A protective layer (called SEI) forms on the anode. During every charge and discharge, it slightly breaks and repairs itself, producing a very small amount of gas.
Slow electrolyte decomposition
Over a long time, the electrolyte may slowly react and create gas.
This kind of expansion is even and slow and usually appears after many charge cycles. It is not immediately dangerous.
What Is Dangerous Swelling (Battery Bulging)?
Dangerous swelling, also called bulging, is not normal and is very unsafe.
| Item | Normal Expansion | Dangerous Bulging |
| Speed | Very slow (months or years) | Fast (few cycles) |
| Shape | Even and flat | Uneven, pillow-like |
| Feeling | Slightly soft | Very hard and tight |
| Cause | Normal aging | Overcharge, overheating, damage |
Can a Swollen LiPo Battery Still Be Used?
No. Never use a bulged LiPo battery.
Here is why:
Internal damage
Bulging means the internal structure may already be damaged, increasing the risk of short circuits.
Chemical instability
Fast gas generation shows the battery chemistry is out of control.
High fire risk
Any further charging, discharging, or even resting may cause fire or explosion.
Never try to fix it
Do not puncture the battery. This can cause immediate fire because air reacts with the battery materials.
Conclusion
LiPo batteries will slightly expand during normal use, so safe design must include extra space. Tight battery cases are dangerous. If a battery shows bulging or hard swelling, it must be stopped and recycled immediately.
Good design and correct handling are the key to LiPo battery safety. If you have any LiPO battery requirements, please don’t hesitate to contact us. We’re pleased to quote our best price for your evaluation.
