Thanks for this! My partner's laptop has started giving battery-related warnings and I - even as someone vaguely technical - hadn't really considered it might become actively dangerous.
If I'm totally honest, I simply and somewhat cynically figured it was a ruse by the manufacturer to bilk some money from us on an unneeded replacement, given its software's likely counting daysSincePurchase!
Modern lithium-ion batteries have a really nice voltage regulator and smart charger embedded within which can estimate cell wear, count charge/discharge cycles, and tell you how much absolute charge is remaining.
It's at least possible for the manufacturer to be using this information instead of simply counting the hours.
If I'm totally honest, I simply and somewhat cynically figured it was a ruse by the manufacturer to bilk some money from us on an unneeded replacement, given its software's likely counting daysSincePurchase!