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I have a notebook which supports USB-C PD charging. I've been using 3 chargers that I have. The battery that came with the notebook (original) puffed up after about 1 year of usage, but I didn't seem to know why. Then I bought a brand new battery and started using only 1 charger because I left the others somewhere else. The new battery started puffing days after I started using the other USB-C charger.

Since USB-C Power Delivery is a standard for charging, I thought at least the notebook is able to negotiate the right current voltage etc for charging. All the 3 chargers support the right voltage (19v) and power (45w or up).

Is it possible that this second charger is causing this problem? By the way, why do batteries even puff up?

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No.

None of the USB specifications involve directly charging the battery, rather they supply power to a battery charge supervising circuit inside the device.

Damaging a battery by overcharging, overdischarging, charging after overdischarging, etc, is the fault of the charge supervisory circuit or a defect in the battery itself, not the external power supply.

That said, it's possible that some faults in an internal battery charger might not reveal themselves if the power supply used were always the limiting factor, but that's far from something you should rely on, especially as overcharging (or otherwise inappropriate charging) could still occur at a low charge rate enabled by a weak supply.

But a "bad" power supply can cause problems - with out-of-spec voltages it could destroy internal circuitry. Or with a failure of isolation it could kill the user.

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By the way, why do batteries even puff up?

Lithium-polymer batteries 'puff up' when some of the electrolyte decomposes into gas. This can be caused by over-voltage, over-discharge, high temperature (ambient or self-heating at high current), poorly formulated electrolyte or mechanical damage.

Combination of high temperature and high voltage exacerbates gassing, so you should avoid keeping the battery fully charged for long periods, especially at high temperature (>25 °C). However depending on the particular chemical formulation it may gradually puff up even at lower voltage and temperature. I have some Lipo batteries purchased around 17 years ago that are still rock-hard. I also have a couple of batteries purchased about 5 years ago that I never used, which have started to puff up. The newer batteries have a much higher 'C' rating, and a different formulation which seems susceptible to 'puffing'.

It's possible that the charger circuit inside your laptop has developed a fault which is overcharging the battery. Alternatively you may just have a bad battery. If the battery is still working, charge it and measure the voltage. It should be less than 4.2 V per cell.

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