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I'm planning to build a DIY Raspberry Pi tablet powered by three 18650 li-ion cells.

I want to be able to use the device and charge the batteries at the same time, like it's common for tablets.

Here https://electronics.stackexchange.com/a/79108 it says:

While it is true that you can't actually charge and discharge a battery simultaneously, it is quite common to have a charging source, a battery, and a load, all connected in parallel so it looks like you are charging and discharging simultaneously.

I'm looking to combine available parts, as I don't know how to create my own circuits. I found the following component on aliexpress:

3S 12V 18650 Lithium Battery Protection Board 11.1V 12.6V overcharge over-discharge protect 8A 3 Cell Pack Li-ion BMS PCM PCB

https://de.aliexpress.com/item/32899770249.html

I could not find a datasheet for the board or the chips on the board, here are the specs listed on aliexpress:

Model HX-3S-03
Overcharge voltage range 4.25-4.35v±0.05v
Size 30302.8mm
Over-discharge voltage range 2.3-3.0v±0.05v
Upper limit working current 6-8A
Working temperature -40---+50 °C
Upper limit instantaneous current 9-10A
Storage conditions -40-- +80 ° C
Quiescent current less than 30uA
Effective life more than 30,000 hours
Internal resistance less than 100mΩ
Short circuit protection protection, delay self-recovery
Charging voltage 12.6V-13V

Would such a board be suitable for my purpose?

Edit: the comments asked for better information, i.e. a datasheet, which I couldn't find. So I added the specs listed on the aliexpress page.

I also found that note on an ebay-ad for the same board:

  1. After connecting the cable, you need to charge it first, then there will be output

https://www.ebay.co.uk/itm/3-String-11-1V-Lithium-Battery-Power-Circuit-Board-for-12V-Electronic-Products-/324302796542

So that sounds if it cannot be used as "load sharing charger" (like @ocrdu pointed out).

bug.spencor
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    You appear to be linking to an AliExpress ad rather than a proper datasheet so most of us won't bother to look at it. See https://electronics.stackexchange.com/questions/504044/what-to-check-for-when-buying-an-electronic-component-or-module for some good guidance on parts purchase. – Transistor Jan 01 '21 at 16:33
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    *Would such a device be suitable for my purpose?* - what device? Where's the data sheet? Do you mean the flaky looking aliexpress thing? Don't you care about quality or reliability or the original source and their manufacturing quality system and product handling system? – Andy aka Jan 01 '21 at 16:33
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    Battery protection boards and BMSes aren't chargers, let alone load sharing chargers, so no, it is not suitable for your purpose. You still should add a BMS board to your battery pack for safety and cell balancing, but you still need a proper charger. – ocrdu Jan 01 '21 at 17:45
  • Thanks for your comments! Transistor Andy aka: I could not find a datasheet. I added more specs from the aliexpress ad; that's all I could find. Of course I'm interested in quality, I just don't know how to properly judge it for electrical components. @ocrdu: OK, "load sharing charger" is already helpful term to continuing my research. Do you have any pointers where to learn about BMSs and load sharing chargers? For my specific board I also found the note "After connecting the cable, you need to charge it first, then there will be output" which seems to confirm your answer. – bug.spencor Jan 03 '21 at 12:52

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