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I have a mobile WiFi router, which contains 3.7 V pouch lithium-ion battery. But I use it only in one fixed location where the charger always plug in. The problem is, the Li-ion pouch cell will puff up in the long run. How can I use super-capacitor (or ordinary capacitor, as it is always power on) together with any circuitry to cheat the device that the 3.7 V lithium-ion battery is there so it will stay on? Thanks in advance.

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    \$\begingroup\$ The problem is, the battery will puff up in the long run. That should not happen. That would point to either a faulty-at-production battery, or at a faulty router, if it happened more than once. How often did that happen to this specific device? \$\endgroup\$ Commented Nov 12, 2023 at 22:23
  • \$\begingroup\$ Why the super-capacitor if you want to modify the electronics to ignore the absence of a battery to begin with? \$\endgroup\$ Commented Nov 12, 2023 at 22:24
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    \$\begingroup\$ You are more likely to break the device doing this than to derive any benefit from fixing a problem that doesn't yet exist. \$\endgroup\$
    – vir
    Commented Nov 12, 2023 at 22:29
  • \$\begingroup\$ Does the device actually not work if you just remove the battery while it’s connected to an external power source? \$\endgroup\$
    – jcaron
    Commented Nov 12, 2023 at 22:50
  • \$\begingroup\$ @MarcusMüller Long time charging will make the battery swollen. I have to replace a few batteries in the past, I don't think the device will stop charging when the battery is full, that is why the swollen battery. The device will stop working if battery is removed. \$\endgroup\$
    – Ryan
    Commented Nov 13, 2023 at 1:00

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I can't answer the actual question about a supercap being used in place of a Lithium battery, but you can try to simulate a battery with a 4V - 4.5V power supply. I'd put a diode in series with the power supply to prevent the battery charting circuit of your router from trying to "charge" the power supply by reversing the voltage at the point the power supply connects to the router. Adding a diode will create a 0.7V voltage drop (for a typical silicon diode) at the router, so instead of 4.5V the power supply is putting out, the router will only see 4.5-0.7=3.8V at the router, which would be within the range of a Lithium battery voltage range (Lithium batteries have voltages ranging 3.3 - 4.2V).

Full disclosure: I'm not an electrical engineer and don't have a EE degree. I just work with electronics and look at schematics a lot as a firmware engineer.

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  • \$\begingroup\$ I have used many li-PO batteries for years and store unused ones correctly at the selling and storage voltage of 3.7V. then they work properly for about 300 charges for years and none pulled up. Recently one battery in a product was puffed up and its voltage was 0V because the product was turned on for a few weeks. A rechargeable Li-PO battery must NEVER be allowed to go below about 3.0V. \$\endgroup\$
    – Audioguru
    Commented Nov 12, 2023 at 23:52
  • \$\begingroup\$ Do you think a resistor + capacitor in serial would do? The question here is just want to get rid of the battery, the device is expecting a battery even it can get power from power source. \$\endgroup\$
    – Ryan
    Commented Nov 13, 2023 at 1:07

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