The common brick lithium battery packs are the least safe because they are very vulnerable to abuse.? That is:? over-charging, over-discharging, shorting, puncturing, and failure to balance the cells.? These are the battery packs that have a main power lead and a balancing connector:
They have no built-in protection.
Cordless power tool lithium battery packs are among the safest because they are encased in hard plastic and have built-in short circuit, over charging, and over discharging protection.? Also, you can't forget to balance the cells because balancing is also internal.
Cheers,
Don
Don LeRoi