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While picking up LiPo battery for my project, I've seen that there are two different types: small and inexpensive one, like this one here that can be charged with a simple circuit like this one. And there are big ones like this one here that require special expensive charger like this.

Why is it like this, if the internal chemistry workings are the same? Why do they need special chargers when the unit cell has the same nominal voltage?

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Batteries first:

The cheap battery is a single small low current cell. Its rated nominal charge/discharge rate is 0.2C (it's 400mAh so that's 80mA). You'd be looking at about 5 (400mAh/80mA) hours to fully charge at the nominal current. It is designed to be used in applications where it discharges at that sort of rate as well.

The expensive battery has a far higher capacity and multiple cells. They also have significantly higher rated currents. They are rated at 20-30C rates, that means applications where the battery is drained in a couple of minutes not the 5 hours of the cheap cell.

So very different batteries for very different applications. One is for keeping a low power device running for multiple hours. The other could do that but is designed for something that takes a lot of power very quickly.

On to the chargers:

The small simple cell/charger will charge a single cell at a fixed (fairly low) rate regardless of what that rate that cell can take.

The more complex system can cope with multiple cells (up to 6) at multiple different rates. That is adding a lot of extra complexity which means extra components and cost. It also includes a housing and user controls, the mechanical parts and then assembly and testing probably cost as much if not more than the actual charger electronics inside it. And since it's being sold as a product rather than a bare component has to be tested to verify it meets various regulatory requirements. That adds further development cost that needs to be made up somewhere.
For 2.5 times the price you get something with well over twice the functionality.

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The difference is quite simple.

The first battery is a single cell. Single cells are quite easy to charge. Also the battery shown is quite small.

The second battery is a series pack. In this battery several cells are connected in series. This is where the problem comes from. Cells in series need a special charger to balance them while charging. Also these packs are much larger making them more expensive.

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Describing the small charger as simple is a mistake. The chip on there is probably quite complex, these chargers are produced in millions for cell phones driving the price down. The larger charger is much more versatile it can handle different numbers of cells and different and higher currents and has much lower production volumes.

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