http://lygte-info.dk/review/Review%20Charger%20Xtar%20MC1Plus%20UK.html
> ‘break’ the circuit if things got dangerously hot.
Hobby chargers (Accucel is one) take thermal probes — with velcro to wrap around the cell being charged.
Never seen one on a simpler charger though.
But for li-ion — remember:
Battery design is still changing fast. Everyone wants to “reduce the likelihood” of thermal runaway.
Here for example: http://www.porouspower.com/