My laptop is almost 10 years old and the battery was mostly in the network mode, so operated with permanently connected charging cable.
The capacity of the battery is virtually in the A and holds in simple operation just 1 hour only.
At the bottom of the taskbar is often "You should replace the battery."
Can it be dangerous to let such a used battery go even further? I would like to keep a battery as reserve for emergency power. And new batteries are expensive. Can anything in the hardware or software break me?
It becomes dangerous only when the battery begins to inflate, then the battery should not be charged in any case and disposed of properly because it could possibly catch fire.
And how do I know that in time?
Look at the battery and if it should be where it should be a flat surface is gone. Just check from time to time.
FYI
How do I know this: work experience
This is not a problem. The battery of my notebook is also almost 8 years old, depending on the usage may last an hour and only has 38% of its capacity.
As long as the battery looks normal and not curved / bloated you can confidently use it for a few years.
Earlier in the quarry were inserted between the wooden pillars, which supported the wall from below and the wall, broken glass. When the wall began to break, the glass crunched first and you may still have a chance to run away.
acoustic, mains-independent pressure sensor…
It is not necessarily dangerous. The performance of the battery will continue to drop.
Look at the battery, if it is "bloated". If so, then dispose of it properly and buy a new one (or a new laptop).
