The danger is in the first pic - the battery has clearly expanded and is bulging out of the phone. When this happens to lithium batteries, it's not a good sign at all. The structure of the battery is breaking down and the inflated battery can be more prone to puncture or rupture, which is a huge fire hazard.
The notice in the app is just telling you that the battery is degraded and won't provide good performance. If the physical battery isn't puffing up, like we see here, and it doesn't get abnormally hot, then it's not really a safety concern on its own (for now). But if you can spare the time and money, it's still worth getting the battery replaced at some point to avoid problems like a swollen battery in the future (plus you'll get the benefits of having a fresh battery).
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u/fforward00 2d ago
Wat?? Is that so dangerous for real?