# Our daily bread, equivalent of 11-37 kg of batteries

A back of the envelope calculation on how many kilograms of lithium-ion batteries we would have to carry around to power us for a day — until the next nightly recharge.

Depending on age and sex, about 8-13 MJ energy are needed for a day’s existence, assuming light work. Lithium-ion batteries are widespread in smart phones, electric cars and other electronics not least because of their relatively large specific energy of 0.3-0.7 MJ/kg.

Given this, our battery pack would weigh between 11 and 37 kg for once-a-day recharge.

Having calculated this, how about body fat, our own kind of storage medium? Population average body fat content is around 20 %, and about 10 % body fat is essential. Assuming a body weight of about 80 kg, this leaves about 8 kg storage fat per person or 8 kg * 39.5 MJ/kg = 316 MJ stored energy.

Even in the best case, that are 451 kg batteries to carry.

## One thought on “Our daily bread, equivalent of 11-37 kg of batteries”

1. Dear David!

I am a PhD student from the University of Szeged, Department of Psychiatry.
You made a post about a DIY fluorescent microscope (http://dm516.user.srcf.net/?p=107#more-107). Because I can not comment there I thought that I could try to make contact with you this way.
We have a Leitz Labovert microscope and we want to make the same conversion what you did and we would like to ask some questions about that.

I hope that this message will reach you and we are waiting for your answer.

Best,

Zoltán