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i have a Bluetooth speaker that uses a single cel 3.7 2600 mah battery but the charger says is 19V and i have read that the max volts to charge 3.7 V is 4.2 V, so how is this possible? now im confused?

thanks for the help :)

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    \$\begingroup\$ Its not a charger, its a power supply. The actual 'charger' is inside the speaker enclosure along with the cell. \$\endgroup\$ – brhans Apr 7 '16 at 16:08
  • \$\begingroup\$ maybe they use a step up converter to drive the speakers, and with the charger plugged in they bypass the step up converter to give more sound power? \$\endgroup\$ – Wesley Lee Apr 7 '16 at 16:34
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As brhans said, the 19 volt adaptor is not the charger, but the power supply. I do not claim to know why the heck they used a 19V supply to run a 3.7V charger, unless it is that it needs a smaller transformer. If you look inside the speaker you will find the actual charger, but it is probably integrated into the speaker's mainboard.

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Audio amplifier designed to operate at less than 5 volt power supply can only be good enough for headphones. For portable speaker, the amplifier needs a higher voltage.

Inside the box there will be a boost converter to step up 3.7 lithium cell voltage to a higher voltage for the louder amplifier.

Thus, as the other answers suggested, the 19 volt is a standard computer power supply chooses to work as the PSU for this speaker. The actual lithium cell charger must be a buck power supply integrated inside the box.

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