✅ Wiring diagram: https://bit.ly/3i6Pzco

Parts and materials:
18650 Lithium ion batteries - https://bit.ly/3J3KCNl / https://geni.us/LqDK
3S BMS board - https://bit.ly/3Q85BmI / https://geni.us/E30JaSC
JST connector - https://bit.ly/3i0cki0 / https://geni.us/BVDujrc
19mm latching LED switch - https://bit.ly/3KwKoP7 / https://geni.us/eOreDJ5
Boost converter module - https://bit.ly/49PImGQ / https://geni.us/lyHuP
Kapton tape - https://bit.ly/3VOhzUj / https://geni.us/VOVm
Heat shrink tubing - https://bit.ly/4c7c9wa / https://geni.us/WZeB
Battery heat shrink tubing (65 mm) - https://bit.ly/3Pizkd8
Cloth tape - https://bit.ly/3PmHukT / https://geni.us/a51Bn6V

Tools:
✅ Spot welder - https://bit.ly/3Uc7O4w / https://geni.us/5ALs1M
TS101 soldering iron - https://bit.ly/3HUzrI9 / https://geni.us/owyDm5G
Multimeter - https://bit.ly/3vS2aKG / https://geni.us/UmrhyYk
Cordless drill - https://bit.ly/4bZg5PN / https://geni.us/A5AZi
Center punch - https://bit.ly/3xslc8u / https://geni.us/o5WBEwB
Wire stripper - https://bit.ly/3T1pVrO / https://geni.us/6epIs
Step drill bits - https://bit.ly/3Pe3fU6 / https://geni.us/xYRx7J
Helping hand - https://bit.ly/3B9mIgt / https://geni.us/Yyqyte

Hi there!
In this video I am rebuilding this quite old but still very capable Harman Kardon Go + Play Wireless speaker. It is equipped with 2 x 30W woofers and 2 X 15W tweeters inside this futuristic looking ported enclosure. There is a USB and Aux ports and external power supply input on the back of the speaker. I do see this as a design flaw of the speaker, but it uses 8 alkaline type D batteries to run it for portability. These batteries are discharged overtime even if the speaker is off since they are slowly drained due to the speaker being kept in standby mode. This makes it quite impractical to swap out the large type D alkaline batteries so often if used regularly. Also the main drawback is that the speaker is put into power saving mode I assume since the bass response is reduced when running on batteries and the overall volume is lowered. Adding to that, the USB port on the rear will not charge other devices when the speaker is running on batteries. In the video I have the speaker's sound quality tested using the battery power (connected a 12V supply instead) against the external 18V power supply.
Once the speaker is opened up, I disconnect the battery input cables and the external power supply input. I will connect the new battery to the external power supply input instead.
The wiring is quite simple. I am using a latching LED switch to cut off the battery power when not in use. The wires from the charging port inside the speaker go directly to the battery. The battery goes to the switch, then to the step-up converter and then to the power input on the amplifier.
The voltage going to the amplifier must be above 14V. If the speaker is powered with less then 14V, it automatically goes into this power saving mode which reduces sound quality. Therefore using the step-up converter I raise the voltage from the battery (12.6V) to 18V, just like the external power supply would provide.
To build the battery I am using six 18650 cells in a 3S2P configuration to produce 12.6V and around 4.5 Ah of capacity. The cells are welded together using the portable Sequre SQ-SW2 spot welder. The welded cells are wired to a 3S 10A BMS module for balancing and protection.
Once the battery is assembled, the speaker can be put back together.

Personally I love how this speaker sounds. Even compared to the next generation Go+Play. Also, this older speaker now has more than double the battery capacity compared to the new speaker which will result in speaker playing without having to charge for many hours.

Thank you for watching!