Building a custom external battery

Sorry the post is so huge
Application: To power a 13" MBP for an extra few hours, this battery must either be able/shaped to fit in a Dual M16 magazine MOLLE pouch, AK pouch, or even in such a way that it can be laid flat, upto .75 inches thick, one foot tall, and ten inches wide.

If this can't fit into an external pouch, this will be sewn/velcroe'd/put in a custom pouch/map pouch that will be flat, rather than box shaped. I'm looking to integrate a battery with my MOLLE backpack, for ease of use. I mainly need a battery for long flights, from the US to China, and soon, for college (I assume). I'm sure I can build a custom pouch to fit on the outside of the bag, or even find a suitable way to attach and easily remove the battery for airport security/other uses.

My end goal, is to integrate this into my backpack, in such a way that it will be able to power an external USB device, carry a USB Hub, and/or a Super Drive since I plan to run with a SSD/HDD Setup. (not all the above during air-travelling, a backpack full of batteries and wires leading everywhere is really really sketchy.) I'd like to have the end result be something like a plug, that may or may not be retractable, come out of the bottom backpack pouch and be able to 'set it down and charge' when I need it to. It may all seem like overkill, but I like to over design stuff. I can get MB Power adapters for cheap here in China, so a few extra mag safe cables are no problem.

I'd like to use Lithium Cells, (ion or poly I'm not sure, my battery knowledge goes as far as airsoft applications, back when LiPoly was unsafe to use).
I've been reading about 'sealed cells', I gather that these are less likely to blow up.
Heat will also be a problem, I'm not looking for 200+ Watt Hour use, just 100 or so, keep it small for now, so I can get the hang of things. At the minimum, I'd like it to be like a 'second MB battery'. I was thinking, a heatsink setup, along with some small fans. Is it possible to have those fans flip on when the pack reached a certain temperature? Or is it better to leave them on all the time? It probably doesn't matter power wise, as long as it consumes under 2-5% total power it's okay for me.

China uses 220V, the US uses 120, I'd like to set this up for 220, and when I build it in the US, just use a converter for 120. A normal 2 prong, non polar plug would be best. I spend 99% of my time in Beijing anyways.

I know almost nothing about power, I barely have a grasp on Amps/Volts/Watts, I understand the formula's and stuff. Right now I'd simply want to build a working device, and then worry about the mathematics of calculating exact runtime/ect ect later. I'm weary of working with batteries, dead or not.

What equipment will I need to test this once it is built, without involving my MBP?

I don't know anything about power regulators, What do I do about the AC-DC converter for charging the main battery? In the pack means more stuff, more weight, more junk, I can live without carrying a charging cable around with me, I just need my bag as light as possible, my back is weird and doesn't like weight. I also understand the thing about the macbook's power settings. My numbers are always way off, as long as I get 6 more hours atleast it's fine, I don't care. It would be nice if it some how could charge my laptop, rather than power it, but it really dosent matter, especially if I use the battery before the laptop's own power is gone. Simplicity is best.



Requirements:
Weight: Less than 1Kg, 2Kg max. I'm looking for around a 2-2.5 pounder.
Battery Increase Req: Goal is at least an extra 4+ hours of battery life, weight can be adjusted to reflect this. (MBP has a 58 Watt-Hour battery, I would like 70-100 Watt-Hour for my battery. Effectively lasting the 13 hour flight.
Price: Under $250 I'm not looking to go cheap, I want to make sure I get quality parts, and make it as small and/or light as possible.
Power: An external AC-DC power converter would be preferable, weight is important.
Low Heat: I'm worried about fires lol, My bag is made out of Codura, with nylon stuff on the inside, might melt.
Package: I'm looking for something interesting to put it inside of. I was thinking originally a PowerBook case (haha) or a "Thick" double DVD case. I'd like something Metal, that wont catch on fire though. Will most likely go inside of a MOLLE pouch depending on the shape
I would like some sort of indicator LED, or a simple Red/Green light to tell me when it is fully charged.


All in All, I'd like to avoid paying for the HyperMac alternative, although I have worked it into my budget. I would rather build one, simply so I can reproduce it for my friends, who travel a lot and have expressed interest in a external battery. If the price and design can be streamlined, being in china, I can probably find someone that can churn out a whole bunch of these on the cheap.

But I'd be happy with the one.

The 13" MBP Idles @13watts according to PC mag.
This is the bag if anyone is interested, it holds a TON of stuff. Plug I'm a big guy, I wanted a proportionally large bag as opposed to a small 'normal' bag. lol

 

The most commonly used LiIon cell (and thus cheapest per unit) is the 18650 cylindrical cell. These are about 1.6 ounces per cell so you could use up to 20 of them and hit your weight limit.

Some specs: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2763 Since you're in China you can probably get these at about 1/4 the price shown here. Each of these cells is good for about 9.6Wh. (Oh by the way, you *do* know that airlines impose a limit on the number of LiIon cells you can carry with you, don't you?) I've ordered cells from Hong Kong, even with the shipping charges it's cheaper than any price we can get in the US...

I use this charger for my LiIon cells http://74.125.155.132/search?q=cach...duct=185+maha+mhc777&cd=2&hl=en&ct=clnk&gl=us but it looks like it's no longer for sale.

Anyway, presumably you're just going to plug the output of your battery pack into your laptop's DC jack. You need to know the nominal voltage for that DC jack, and arrange your cells so that the voltage adds up to be the same.

E.g., LiIon cells are nominally 3.7V each; if your DC input jack wants 19V then you want 5 cells in series. To get more capacity you then wire multiple strings of 5 cells in parallel. This will make the most efficient use of your battery power, but it will complicate things when it comes time to recharge. E.g., that Maha charger I pointed out will only charge up to 4 cells in series, 14.4V. With 5 in series you would need to find some other charger instead. And charging LiIons is tricky business, you can't just build a simple constant-voltage or constant-current power supply to do the job. As an alternative, you can wire the battery pack with only 4 cells in series, summing to 14.4V. That allows you to use an off-the-shelf charger, but you'll need to add a DC-DC boost converter to bump the pack output from 14.4V to 19V. Boost converters these days can be very good, over 95% efficient, so you're not sacrificing too much runtime going that route. All of the components you need are available off the shelf, you just need to search electronics catalogs to get them...

And also keep in mind, when a laptop battery pack malfunctions and flames out or explodes, it can be pretty nasty. If you're building a pack with twice the energy of your internal pack, you get twice the potential destructive power to worry about.

Be careful if you choose a metal container, to make sure the interior is completely sealed with an insulator/plastic, to avoid short-circuiting on the case itself.

edit: you may find a suitable charger here: http://www.all-battery.com/chargersandbalancersforli-ionli-polymerbatteriesandpacks37vto60v.aspx

 

When rechargeable 18650 is fully charge, it gets to about 4.2V where as primaries starts at 3.6-3.7v when new. There's a lot of fluctuation thus you'll need a regulator.

anyways.. high capacity protected 18650 cells are cheap. They're $2.50 each. Just spend 25$ on 10 of them and you can get about 150Whr from them.

 

www.digitalcamerabattery.com

spendy, but very rugged (very!). I've used their cells on mountain tops as well as +130f deserts. Never a failure.

Their batts have built-in voltage regulation and with the correct adapter cable, can power just about anything from 5 to 25 volts.

You most definitely want to invest in a pack that has internal voltage regulation. LiIon batteries have a steep & sudden voltage fall off curve. No matter what kind of hybrid serial/parallel matrix you wire them up with you'll never, ever get the kind of power output the cells should add up to. On top of that, LiIon cells can very easily be killed dead by deep-discharge. Often all it takes is one overcharge and/or one drain to empty discharge to kill a couple of hundred dollars of of (toxic!!!) batteries. A voltage regulated battery pack prevents all of that. This is the difference between the DIY/sub-$100- packs and the >$250 packs. The DIY and sub-$100- packs are considered disposable. The $250+ packs with voltage regulation will give you 1000 and more charge/useage cycles. Say 5 years of service.

One power pack to bind them, one power pack to rule them all!!

 

# 60 Watt, 16.5V-3.65Amp

Is what a website said about the 60w charger.
I was looking at for example: (this http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2741) and it looked like something that I'd rather buy over making my own.


For an example, how would I wire the pack if I had 10 cells?
10 cells seems pretty small, especially if they are around or even 2x the size of AAs.

I understand charging might be tricky.
What about a power board thingie? Can I get these pre made anywhere?
I'm really good at building things, but no matter mow much I try to learn, like about power, I can't get it. I'm retarded when it comes to power. I'm starting to get MaH and Amps and Volts ect. I knew those from my airsoft days. In airsoft I built quite a few battery packs, just 7-8 NiCad cells with Deans connectors, at the time they were only as big as 3800 MaH so I used those. Shrink wrap the thing, and throw it into my Famas and away I went. Simple.

Like I said my goal is 1-1.5x the current size of my battery, bigger might be better, but if bigger makes it more complicated to wire/charge/ect, then I'd just be good with a smaller size. This is my first pack, I'm sure once I get one working and stuff I will be able to expand to bigger and bigger ones.

 

The laptop will already have a regulator on its DC input. No point in double-regulating...

 

So how would I do the wiring for this?