I'm making a portable speaker setup that can be powered and charged at the same time by a regular 19.5v laptop charger. I'm kinda noob with electronics, so I'm not sure if this setup will work as expected. Anyway, the system runs on 4s 18650 batteries, the (protected) batteries are charged via a stepdown converter to 16.8v@2A (suitable for charging). There is a diode to prevent the current from bypassing this buck converter when charging. The other diode is to prevent current coming from the battery to protect the buck charger (I'm not sure if this is necessary though). Does this circuit look alright? will it work? Any suggestions, and/or improvements are much appreciated. Thanks in advance!

Here's the schematic:

 

There are definite problems with this concept. I suggest you read the attached information on charging Li-ion batteries. This is one paragraph from it:
"Li-ion cannot absorb overcharge. When fully charged, the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To minimize stress, keep the lithium-ion battery at the peak cut-off as short as possible. "
https://batteryuniversity.com/index.php/learn/article/charging_lithium_ion_batteries

 

You need to use an appropriate BMS for the battery charging.

 

There are definite problems with this concept. I suggest you read the attached information on charging Li-ion batteries. This is one paragraph from it:
"Li-ion cannot absorb overcharge. When fully charged, the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To minimize stress, keep the lithium-ion battery at the peak cut-off as short as possible. "
https://batteryuniversity.com/index.php/learn/article/charging_lithium_ion_batteries

Yes I know I need a 4s bms to cut of the batteries at 4.2v. But what I'm questioning bout is this: I want to charge the battery at a constant current while supplying power to the load (when charging). But connecting the charger directly to the amp creates a second path from the charger to the battery and thus current will bypass the buck charger. So to protect the battery from charging to fast, at to high voltage ,my idea was to add a diode to prevent this reverse current. I don't know if this would work as expected, and mabye there are better solutions to achieve same result that I don't know of.

 

Yes I know I need a 4s bms to cut of the batteries at 4.2v. But what I'm questioning bout is this: I want to charge the battery at a constant current while supplying power to the load (when charging). But connecting the charger directly to the amp creates a second path from the charger to the battery and thus current will bypass the buck charger. So to protect the battery from charging to fast, at to high voltage ,my idea was to add a diode to prevent this reverse current. I don't know if this would work as expected, and mabye there are better solutions to achieve same result that I don't know of.

There are "UPS" boards set up to charge and power at the same time. They come in many configurations.

 

There are "UPS" boards set up to charge and power at the same time. They come in many configurations.

Thanks I'll have a look at that. Lol I accidently logged in with wrong google account haha wow