portable power for laptops

I have a HP laptop. When I first bought it, the battery life on it was decent.
Now the battery on it only lasts like 1 1/2 hrs.

I was thinking about buying a mac book pro since the batteries on those laptop last a long time.

I have a friend who has an iphone and he bough a cool iphone case for it.

When the battery on his iphone is almost out of power. He switches to the power supply on his iphone case and that gives him extra power.

Do you guys know if they sell something like this for laptops. You know like a portable power supply. So if I'm at starbucks and my laptop battery is almost empty and I'm not near a wall plug I can just get the extra power supply from my laptop bag and plug it to my laptop?

I know I can just buy an extra laptop battery, but do they sell something for windows pcs that lasts long?
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Yes, there are quite a few different options to choose from, you can just do a search for Portable Laptop Battery. Personally I prefer ebay and amazon because of their prices. A lot of times you can find them new there as well.

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