You are correct in regard to a large capacity 12v battery having a larger equivalent energy capacity vs. the IMA pack.
In regard to high voltage and safety I'd like to expand and clarify your statements so those reading will have the best information
AFAIK to protect themselves.
There is basically no difference in the level of danger between AC & DC voltage.
Voltage ranges from 6 - 600v _tend_ to be the most dangerous because of the relationship if voltage and resistance. The body has a natural resistance in ohms and voltages below 6v _tend_ not to have enough "punch" to deliver a significant enough flow of current.
Voltages above 600v _tend_ to cause involuntary muscle reaction and release you from the source (assuming its something you've grabbed with your hand).
Voltages above 100,000v arc and follow you across the room regardless of any muscle contraction and your literally cooked.
The path that the current takes through the body is the most significant factor in regard to your arrival at the Pearly Gates. Paths across the chest have a much greater ability to cause the heart to go into v-fib (ventricular fibrillation), an irregular beat that pumps little or no blood through the body.
Voltages passing through the body tend to interfere with the body's own "electrical" system and block the ability to control muscles. The speed of our body's electro-chemical system is _much_ slower than electricity in a conductor therefore there is _no_ time available to react to a "sensed" electrical shock and disconnect from it.
HTH! :)