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Can't get a clear answer anywhere. Need to replace small batteries in small sports mp3 players. They had 150-190 mAh Li-Ion batteries. All I can find are Li-Po replacements. Can I charge those the same way as a small Li-Ion battery, from USB port or 0.5 A charger or do I really need a special charger for those?

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  • \$\begingroup\$ Special charger unfortunately since the termination voltage is slightly lower. \$\endgroup\$
    – winny
    Jun 1, 2022 at 7:05
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    \$\begingroup\$ To answer your question as it's written: yes you can charge them from USB. But you need to do so with the correct USB charger. \$\endgroup\$
    – Puffafish
    Jun 1, 2022 at 7:11
  • \$\begingroup\$ USB port is not a charger. USB port is for a power supply. The device with battery has internal charger. \$\endgroup\$
    – Justme
    Jun 1, 2022 at 12:37
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    \$\begingroup\$ It sounds like you want to remove old Li-Ion batteries from mp3 players and replace them with Li-Po replacements that are the same capacity (150-190 mAh). That should work fine. The mp3 player must have a charger already built-in to charge the Li-Ion cells. The same charger will work fine with Li-Po. The charger will never know the difference and the Li-Po will be happy. \$\endgroup\$
    – user57037
    Jun 2, 2022 at 4:54

2 Answers 2

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They had 150-190 mAh Li-Ion batteries. All I can find are Li-Po replacements.

What you call "Li-Po" IS a Li-ion cell. It's a pouch Li-ion cell, but a Li-ion cell nonetheless.

Can I charge those the same way as a small Li-Ion battery,

Yes, because it is a Li-ion cell.

from USB port or 0.5 A charger

From a charger, yes. Not directly from a USB port. You need a charger between the USB port and the cell.

Though, 0.5 A is too high for a 190 mAh Li-Ion cell. You should find a 0.1 A charger instead.

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First, as people already noted, your "USB port" or "USB charger" are not Li-ion chargers, they are constant-voltage (5V) power supplies, maybe with some limitations. Your MP3 players, however, must have a built-in proper Li-Ion charger circuitry, so the type of power source does not matter much.

However, you need to seriously consider the VOLTAGE rating of your replacement. Li-Po stands for "Lithium Polymer", which refers to differences in mechanical construction and separation materials of the cell. But the exact chemistry might differ between your old cells and the new one. The old-fashion Li cells used to have charging voltage of 4.2 Volts, some modern one use 4.35V to reach maximum capacity. Some other Lithium families use max charging voltage as low as 3V. So if your new battery has lower max charging voltage rating, use it with higher-voltage chargers could pose a fire hazard for your devices.

If the voltage rating of the new cell is higher than for your old ones, the charging circuit in the player won't provide full charge to the new cell, so playtime might be less than expected.

On the last note, nominal cell capacity makes no difference whatsoever on charge process, the cell will be charged to max capacity automatically, because the charge termination in Li-Ion charging algorithm is based on low-current cut-off, which will occur sooner or later, proportionally to battery capacity.

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