My rustic writer's retreat: portable power (part II)

My rustic writer's retreat will need portable power. Why? Because hand-cranking a margarita is a real nuisance.

Power is also important because ... after interviewing dozens of people, transcribing hours of tape, collecting a mess of files, and jotting lots of inscrutable notes, the only way I can reasonably bring order to the chaos of my reporting is with some kind of tried and true information management system. Every reporter grapples with arranging and organizing information, and it's a topic I hope to cover here down the road. What's important right now is that my system requires a computer, and computers require power.

Like a MacBook, only worse!

So how many D cells am I going to need to get out of the house and into a campsite that has all the amenities of home? I'm going to figure this out like the philosophy major I was. I exist. "I" is a person who uses a computer all day. Therefore, I tend to recharge my HP Spectre XT from a low charge of ~10 - 15% to a full charge three or four times during working hours. I think that's Kant.

Three or four charges per day accounts for using internet and not being too conscious of power consumption factors like screen brightness and background porn ... for ... an article ... so I'm betting I can get that down to two or three charges daily. If I camp for two nights, three days, I'm looking at six to nine charges over the course of my DIY rustic writer's retreat.

Of course, that's all meaningless if I don't know how much actual power I'm using. I'm a little out of my league here, but this is what I've pieced together. Caution: light math ahead.

Power brick

The output from my laptop's power brick is 18.5V @ 3.5 amps. Science!

But what does that mean? Since the mystics that inscribed these odd characters have been silenced, we'll have to do some internet learning. To make this easier to grasp, let's start by looking at one of the popular portable power options that's available off the shelf, and then work backwards to see if it suits our needs. Introducing the Micro-Start XP1.

Micro-Start XP1

The Micro-Start XP1 is a smallish lithium ion battery, same as in your laptop. Lithium is the lightest metal around, which makes these batteries substantially more portable than lead acid numbers, like the one in your car (lead is not known for its lightness, nor its digestibility). The XP1 is a little spendy, but the issue at hand is storage capacity. How can I know if it'll meet my power needs?

Like my laptop power brick,  the XP1 is covered in lots of strange symbols. My honed journo instincts are telling me that all these numbers are related. I think Woodward and his bear friend had similar instincts about a hotel in D.C. One of the numbers on the XP1 tells me that it has a 44 Wh (watt-hour) battery. In other words, the XP1 could theoretically power a 44 watt device for an hour. That's the amount of energy it has.

Here's where it gets mathy. This dude named Ohm tells us that power = voltage x current. We actually have two of those variables already. The voltage I'll need, according to my laptop power brick, is 18.5V.  We know the XP1 has 44 Wh of energy, which means 44 W (power) for an hour (time). Let's just tuck that pesky hour under the rug for a moment, but keep it in mind. Now let's plug in our variables.

power = voltage x current

44 W = 18.5V x ??? amps

If you do the simple division (with a calculator, duh), you'll find out that this battery can deliver 2.4 amps @ 18.5 volts. That's not terribly useful information unless we factor in time. Someone hand me that hour we tucked under the rug. If you chuck that hour as hard as you can at those numbers, you get something useful. This battery can give 2.4 amps for one hour @ the required 18.5 V. In other words, this is a 2.4 amp-hour battery. Therefore, ecumenically speaking, God exists. I am God.

Boom. Philosophy.

Now let's turn back to my laptop. The time it takes to charge my laptop varies, but to make this simple we'll say it normally takes one hour to charge from nearly dead to 100%. According to my power brick, the most current my laptop will draw is 3.5 amps. That's a maximum draw, so the computer probably needs less under normal conditions, but we'll use that number to be safe. If it takes one hour to charge my laptop, and the laptop is drawing 3.5 amps for that period of time, I'm going to need a 3.5 amp-hour battery for a single charge. Sweet Moses, I do believe we now have two figures we can compare side-by-side.

And ... holy crap, this battery doesn't even come close!

The XP1 has a 2.4 amp-hour battery, which means it won't even charge my laptop, which needs 3.5 amp-hours of energy to go from dead to fully charged, even once. In reality, it probably would give me a full charge since my computer wouldn't be sucking the maximum 3.5 amps under normal charging conditions, but that still only leaves us with one recharge, and for this booze swilling DIY writer's retreat to work, I'm going to need to recharge the laptop six to nine times.

Like the man said, you're going to need a bigger boat. Also, dude, where's my car?

Car battery

Up Next: A big ass car battery