I purchased a quadcopter for my daughter a year ago from Brookstone, the "Flight Force HD". Nice little copter, but what I thought was a nice feature, appears to be a fatal flaw.

The quadcopter has a battery module that slides in. I thought this was much nicer than other inexpensive copters that have a loose wire battery connector to plug together. Better for my 10 year old daughter.

However, when the battery pack failed, I learned that you can't buy a replacement. "no problem", I said. Certainly I can source a 3.7V LiPo battery, which I did. But the known good battery it didn't bring the battery pack to life.

The Brookstone people were nice enough to replace the whole quadcopter. I confirmed that the new battery pack operated the old quadcopter just fine.

Now I'm wondering what exactly went wrong. The only thing I can think of is this small board, which is part of the battery pack. It's some kind of charging regulator, I think.

It has a capacitor, a couple resistors, then four SOT23-6 components. Three of them are labeled "8205B", which I think is a MOSFET.

The real mystery is the device marked "5171Y". I have looked very close and that definitely is the marking. I've googled for at least a couple hours and can't find it. It has a vertical stripe across the device to the left of the "5". Anyone know what this device is?

In the second picture, it's the SMD on the far left.

Of course, my fear is that the thing will fail again. The reviews on Brookstone's web site are full of complaints on this problem.

 

The Brookstone people were nice enough to replace the whole quadcopter. I confirmed that the new battery pack operated the old quadcopter just fine.

Of course, my fear is that the thing will fail again. The reviews on Brookstone's web site are full of complaints on this problem.

Brookstone knows there is a problem, take the second one back when it has a problem, I'm sure they will replace that one too.

As for your chip, it is likely a dedicated LiPo charging chip. TI and most other manufacturers make them - including small semiconductor companies in China that we will never track down.

 

Brookstone knows there is a problem, take the second one back when it has a problem, I'm sure they will replace that one too.

As for your chip, it is likely a dedicated LiPo charging chip. TI and most other manufacturers make them - including small semiconductor companies in China that we will never track down.

Thank you for your thoughts. Turns out that specific drone is discontinued (imagine that!).

I think you're right about the charging chip. I suppose I need to investigate if I can bypass the whole circuit. That is, maybe this is only needed when charging and not when the battery is in use in the drone...

 

I need to investigate if I can bypass the whole circuit.

Unwise. Lithium cells need monitoring (by the IC) to ensure that neither charge nor discharge limits are exceeded. Failure to do that could result in fire or explosion.