Ok, my fault, I'm sorry for offending you
Well - there is an emergency shutdown - well, not a real shutdown, more like instant power off - as soon as the battery voltage drops below a sanity treshold.
Normally, the OS monitors battery voltage drop over time and tries to estimate remaining capacity. Depending on the condition of the battery, this drop is more or less steady and smooth.
100% corresponds to a maximum voltage a healthy li-battery has when fully charge.
If it shows 70% right after charge, I suspect your battery has died. Either by a total discharge or because it was faulty from the beginning.
But you can try to "revive" it by repeatedly charging / disconnecting to squeeze more juice into it...
In the wiki there is a link to a battery calibration tool which shows the voltage.
Could you please tell us the voltage of your battery when fully charged and charger disconnected?
Does it drop rapidly then disconnected?