Pedalling with a battery on one's back

How easy, common and safe is it to carry a battery in one's backpack as in this clip?
https://www.youtube.com/watch?v=RK38Nw_KNmY

Though I didn't watch the clip, ask yourself, "would I carry gas on my back?" the answer should be "NO", so many more chances for shorting failure.
Granted, most batteries won't spill, but first and foremost in any powered transport is the "affixing the fuel to the frame for safety" concern.Find one form of common transport where the tank is removed for filling.There are safer packs now, but look up lithium battery explosions on youtube, if it were on your back at speed you probably wouldn't know until the backpack was melting on you, at that point you're going to get some serios burns unless you have a seatbelt cutter on hand, and can use it surgically with speed.
If not for the sake of safety, it would be rough on your back.Though it can be done, it wouldn't be smart.

You're right.After seeing this
https://www.youtube.com/watch?v=7-xPHopebiE
I wouldn't want an Li battery on my back!