Step 5: The Batteries
NiMH batteries are the kind you see that power RC cars. They come in battery packs, and need no special circuitry to charge them. They are very heavy.
Li-ion batteries are very common. They power laptops, portable DVD players, cell phones, etc. They are very lightweight and have lots of mAh, meaning that they can power a portable for a very long time. They require special circuits to charge them.
Conventional batteries are what you use for all sorts of electronics. These batteries are your standard AA, AAA, 9v, D, and C batteries. These are relatively cheap, but they aren't rechargeable. (Unless, of course, you buy rechargable ones.) Conventional batteries can get expensive over time, and they are a little heavier than other types of batteries.
As you can see, all types have their pros and cons. For NiMH and Li-ion types, there is a rule.
You can get batteries that are:
If you want to choose NiMH, then you don't have to do much for them. They are cheap, and to charge them, you just feed power straight to them. Dead simple. Unfortunately, they are often heavy and big.
Li-ion batteries are great, but require a bit of work. They need special charge protection circuits. They cannot be shorted or overheated. Despite these things, they are very worthwhile. They are small, thin, lightweight, and long-lasting. The bad part is that they cost quite a bit.
WARNING: If you do not have a charge protection circuit, Li-ion batteries will EXPLODE. These batteries are dangerous if not used properly. They may not be shorted, overcharged, or undercharged. If you are buying Li-ion batteries from eBay, you MUST buy a Universal Battery pack. These battery packs have their own built-in charge protection circuits and often have charge indicator LEDs. If you do not know much about Li-ion batteries and their various protection circuits, then you MUST use NiCD.
Conventional batteries are great for the "average joe." They are readily available and are easy to use. But, unless you get rechargeable ones, these can cost quite a bit in the long run. The good thing is that these batteries come in many shapes and sizes to suit your needs. If you're going with conventional batteries (Like AAA's, AA's, C's, or D's), then you need to pick between battery life and weight. AAA's will be very light, but have a short battery life. D's will give you many hours of playtime, but they are extremely heavy. AA's and C's are in between.
There is one more important factor: mAh. mAh stands for Milli amp-hours. The mAh of a battery is how many mA that battery can provide for an hour. If a console and screen that together consume 1,000mA is being powered by a 1,000mAh battery, then that portable would run for 1 hour. Find batteries that have a high mAh. Batteries with 3,500 will run an NES portable for about 3 hours.
To find battery life, add the mA consumption of the console to the mA consumption of the screen. Divide that number into the mAh of your batteries. This may all sound confusing now, but the more you work with the batteries, the more it makes sense.
Here is a useful topic that has the mA consumption of many consoles and battery life estimates for them.
Now we can finally get started on this thing.