Those are pouch batteries, they never need a hard shell. Each one will have a tiny PCB with protection circuitry on it. It’s the only way to prevent them from

Those are pouch batteries, they never need a hard shell. Each one will have a tiny PCB with protection circuitry on it. It’s the only way to prevent them from accidentally catching fire or exploding. Batteries are far more complex than most people expect. Especially lithium batteries found in phones. The chemistry is super sensitive, and anything except careful monitoring of each battery pack risks catastrophic failure. Hence the tiny PCB on each battery pack.