I am building a blue tooth speaker. I would really like to make it able to charge my milwaukee m18 batteries when ac is available and use the batteries as a power supply when not plugged in. Like a laptop or a cellphone. Would this work?

For multiple battery slots use a relay board to isolate the battery for the speaker? Is there a better way?

I intend to use the electronics from the milwaukee charger for charging the milwaukee batteries. I am not very good at design but I can get the correct components to work together. The speaker is powered by a 200w class d amp rated 12-24 volts. The kit came with a 3s power board. I would like to use that as a power bank for a couple USB slots and a type c slot power bank.

What I am worried about is the safest way to switch the batteries to charge mode and switching the amp to a different DC power source. I am also worried about the multiple charging slots safely only using 1 battery to power it when both batteries are in. That's the jist of it. Any input would be greatly appreciated!


Yinhing Power Supply Controller, DC Power/Battery Switch DC 12V 24V 36V 48V 10A Power Supply Battery Controller Emergency Automatic Switch Module

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I am sure that you have a very clear picture of your proposed system in your mind but I find your description a little difficult to understand. Can you draw up a simple block diagram of it with a few labels to give us a better understanding of what you are proposing?
Just a note: That 200W spec for the amplifier is just advertising. With a 24V supply and 4 ohm speakers you will get an absolute maximum output of 70W per channel.

 

Will do!