Permanent charging of battery: harmful?

SanDisk MP3 players Sansa® Clip | Sansa® Clip+
1

I wander if keeping the Sansa Clip connected to a car 12 volt USb connector is harmful for the battery.

This will charge the battery if it is empty, but what if the battery is already full? Can it harm the battery?

My purpose is to have it playing for several days on end.

Any clues?

2

I’ve asked the same (or similar) question elsewhere, and typically hear back that “modern portable electronics with rechargeable batteries have onboard circuitry to control the flow of charge (and also to shut down when internal charge is low).”  In other words, if you’re supplying a reasonably sized charge, the Clip will take what it needs.

That’s what they say, anyway!

-Matt

3

While it’s true that players turn off charging when the battery is charged, they turn it back on again when it goes back down a little so it’s getting charges a lot more than it should.  That tends to shorten their life somewhat.

I know with laptop batteries leaving the battery in the laptop all the time when it’s always plugged in shortens the life of the battery enough that most people will replace it if they need to use it in a year or two.  My experience with laptops has been that the batteries last 3 to 5 years if I don’t let that happen and a year if I do.  Of course the laptop is still usable and the battery doesn’t die totally so as long as it stays plugged in it doesn’t matter much.  But I generally remove the battery while it’s plugged in.

I haven’t left an MP3 player plugged in that long but they’re the same type of battery (Li-ion) so presumably the same thing will be true.  But if you plan to always leave it plugged in it might not matter what happens to the battery.

Barry

4

The problem with the laptop is not the charging of the battery but the heat produced by the laptop itself. 

See also here: http://en.wikipedia.org/wiki/Lithium\_ion\_battery#Guidelines\_for\_prolonging\_Li-ion\_battery\_life

5

Lithium ion batteries have circuitry to shut down charging when they are full, if they didn’t they’d explode.  Not a good thing.  NiCd batteries did not like a partial charge but that doesn’t harm a Li Ion battery.  It might actually prolong the battery life because it is the number of complete charges that determines their life as well as calendar time.