AliExpress doesn't 'sell' products, they are more like a marketplace of sellers from China, much like Amazon. And you're right - it's a crap shoot on what you get coming out of china - some of it is really good, some of it not so much.
My extensive experience with batteries is with12V lead acid for cars boats and RV's, and Lithium Polymer packs - these from playing with RC crawlers, or 'tiny trucks'. "LiPo", as they are referred to, are considerably more volatile than lithium-ion, like we have in our ebikes. For lipo cells, each cell has a sensor wire that the charger uses to balance all of the cells in the pack. These packs are generally 2 to 6 or so cells, 2 or 3 being most popular for crawlers - low power - and more for high speed surface and aircraft models, like racing cars and boats, and electric powered aircraft. AFAIK the only way to get proper cell balancing is with this sensor wire that actually measures the voltage of each individual cell. Obviously our bike batteries don't do this, and there are a lot more cells, like 50 or so. So as I understand it, our very basic chargers and battery management systems (BMS) only measure for whole-pack voltage, min and max for shut off. There isn't really any true balancing going on there. And why simply charging up to 100%, or 'peaking' out the pack, is the best way to keep all cells balanced. If too many are failing, or are of lower capacity - measured by voltage - then the whole pack suffers, those bad cells will drag the rest of them down. Also why it's valuable to charge the pack fully - the best chance of peaking up all the individual cells.
Same way a lead-acid fails - if one set of plates, or 'cell' fails, it drags the others down to it's level, the whole battery fails. And why you don't mix old and new deepcycle batteries in an array, like in RV's and boats and such. I've seen charge systems destroy a good battery paired with a bad one - starting batteries for a marine engine. It literally cooks the juice out of the good battery, trying to get the bad one to take up charge.
Anyway, that's how I understand it, and these are kind of low-tech packs for our ebikes, much like you find in any cordless appliance, but just a lot more of them, and why you just charge and go like your dust-buster. The charging system is just a very basic process of adding charge amps to the pack. All the BMS does is shut it down at low voltage, and stop charging at high voltage - there isn't really anything else going on there.
