Becoming Batman: The Possibility of a Superhero by E. Paul Zehr is not a guide to becoming Batman. It would be a more interesting and significantly longer book if it was. The book concentrates on the physical aspects, namely could someone physically fight crime as Batman is depicted to in the comic books.
Were it a guide to becoming Batman it would likely suggest subjects to study such as forensics, criminal psychology, chemistry, and other sciences one would expect the worlds greatest detective to know. It would explain how to hide the expenses for the gadgets (planes, cars, helicopters, etc.) from the government and possibly depending on continuity the embezzlement (Batman had paid for the Justice Leagues watchtower by hiding it in his companies space budget in one of the animated series). How to avoid being arrested for taking the law in your own hands/assault and explain away the purchases of things like bullets used in the vehicles. It might cover how to explain away injuries acquired fighting, after-all, people would start to wonder how all the injuries came to be (this is done with varying degrees of believability in the comic explanations like falling down the steps while drunk, totaling one of Bruce Wayne's cars to explain the damage done by Bane, and in a spoof saying he was into BDSM). It would explain how to build a state of the art cave underneath your house in secret (the best explanation I have seen was in a Batman novel, not graphic novel, in which he had people, multiple groups each doing a different part, shipped in from a foreign country under the cover of darkness blind folded and in a 18 wheeler then returned them to their home country done this way so they did not know where in the world they were or exactly what they were doing). Though there is other things I have not mentioned.
That said, it is not a bad book and is fairly informative. Though some would probably say needlessly so and it uses rhetorical questions far to often in my opinion. It reads like it is meant to be a text book that uses the Batman angle to make it more interesting for the students (considering the publisher, John Hopkins University Press, that may very well be the reason for the books existence).
The book is divided into five parts. Part one titled Bat-Building Blocks talks about body composition (things like lean body mass, fat, genetics, etc.). This part of the book in particular is very science heavy, explaining things like how cells are made, genetics, nature vs nurture, hormones, etc. ultimately this part of the book states that many factors that are a key to physical performance (such as oxygen uptake) have a genetic performance (usually around 20-30% but in some cases up to 50%). What that means is that your maximum physical potential is in part predetermined by your genetics.
The second part of the book is called Basic Batbody Training. This part of the book is on physical training and goes into quite some detail on how muscles work, limits of toughening the body, and how many calories and what foods Batman would likely need to eat. What I found most interesting in this section of the book is the discussion on the difference between strength and power. It states that strength is the ability to lift large forces regardless of the speed of contraction whereas power is effort at high speed. Makes mention that it is possible to be very strong but not powerful though a certain amount of strength is needed to be powerful. The part on bones is alright most interesting part of that is that while you toughen some bones correspondingly other bones weaken. States that Batman would take vitamins, supplements, have an athletes diet (higher carbohydrates than a non athlete around 60% carbohydrates, 25% protein, and 15% fat), and because of energy expenditure would have a high calorie diet (estimates 3,500-4,000 calories a day). One part of this section I do not agree with. It mentions the importance of calcium and says we should all drink our milk. I like milk, drink quite a bit, but milk is really not as good a source of calcium as it is touted to be. For example: One 12 year study, by the American Journal of Public Health, found that women who drank more than a glass of milk a day (the USDA recommends three per day) had a 45 percent greater chance of a hip fracture. Women who got the same amount of calcium from non-dairy sources had no increase. This is not the only study that points to milk not as good a source of calcium as it is generally thought of there are others as well. The reason speculated for that is that they are getting too much protein (which milk has). The human body uses calcium while processing protein, the amount of calcium in milk is not high enough to counter the amount of protein the average person eats which leads to the body leeching calcium from the bones.
The third part of of the book is named Training the Batbrain. It starts by explaining how the brain and nervous system work (somewhat) and how training optimizes reflex pathways and motor learning. It then talks of over-training and how you have to practice often to maintain the skills. The next chapter (Each part is divided into multiple chapters) deals with the type of martial arts training Batman would likely learn to fight crime. It starts out mentioning, often seen on forums, that Batman has studied 127 martial art styles. The authors sees this as hyperbola. That it is impossible to master that many styles, is pointless since you wouldn't gain deep understanding or competency, and that he does not think there are that many truly different styles (though there are subdivisions of martial arts that would put the number into the hundreds). I sort of agree with him on that. The thing is I think it could be done, not grandmastery or even mastery in each style, but it is possible to study the styles to find out how they differ from one another learning the strengths and weakness's of each. Mastery is not needed but knowing the styles could help you prepare to combat those styles (much easier to do when you have an idea as to what your opponent is likely to do). The book mentions that most modern day styles are really not good at combat; having been made less martial (Judo for example had open hand strikes and kicks before it was commercialized). Suggests that Batman is most likely to learn Ninjitsu, not the fake version, the actual version that was in Japan during the 18th century that involved espionage and assassination. He would need a style that involved multiple styles of combat including punching, kicking, throwing, grappling, joint locks, and weapons. Most fighting styles specialize in one type such as Judo having throwing and grappling but no striking. The last chapter in this section deals with the question can a person go around fighting without killing his opponent. Books answer is much easier to kill but could be done provided he was skilled enough.
The fourth part of the book, Batman in Action, deals with the damage Batman can do and still continue doing what he does, hardening the body (which was discussed in part earlier in the book), and night shift work. The first chapter in this part talks about the weak spots in the human body, power of a punch/kick, and taking a fall. Talks about body hardening techniques such as hitting an object repeatedly. Then goes into some detail about changing bone density, hardening the skin, and changing the perception of pain. Mentions that Batman is unlikely to do extreme body conditioning because of his suit and some of the side effects (like a loss of manual dexterity). Since I find this very interesting I will mention the part about Mas Oyama, the founder of the karate style Kyokushinkai, who did extreme body conditioning and would have found the breaking point technique seen in the Ranma manga as training he would have done. He repeatedly punched hard objects until the skin broke and tendons were exposed, doing this repeatedly led to callus forms anchored to the tendons (he also did this to other parts of his body by kicking or throwing himself at hard objects). Mas Oyama wrote a couple books that I might look at called What is Karate and This is Karate simply because I find his body conditioning interesting, though I would not do it). The last part talks about the circadian rhythms and how Batman could not only sleep for an hour a day as he is sometimes portrayed to do in the comics. Though the book does not mention the drug Modafinil an anti-sleep drug that allows you to stay up safely for almost two days while remaining practically as focused, alert, and capable of dealing with complex problems as the well-rested; or really any other drugs besides steroids that Batman could theoretically use.
The last section of the book is called a mixed bag and is about whatever else the author felt like talking about. He mentions injury and recovery, gender differences between males and females, and how long could Batman do what he does. Talks about broken bones healing, torn cartilage, having to retrain to get back into shape, and other things. Asks if Batman would use steroids (not likely). Mentions that Batman could not keep up his life style for very long probably only a few years a decade at most.
Interview with the author by Scientific America: Dark Knight Shift: Why Batman Could Exist--But Not for Long
Somewhat related forbes article about the estimated costs Batman inures: Being Batman