Is it good to leave rechargable things plugged in?

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I killed a $175.00 12-cell battery for my laptop by leaving the machine plugged in 24/7 for a couple of years. It was a spiffy lithium ion battery, not the old NiCad.

I think chargers can be built which avoid the problem, so the question is does your device have such a charger.

related, but the so call “trickle chargers” for car batteries that are supposed to maintain charged battery over long storage times should not be left unattended for weeks. I have read that on for a week off for two weeks if cars are not started during long term storage.

@Austinlad‘s link is good info.

Two things have changed since the early days of rechargeable batteries. First, Nickel-Cadmium batteries have been mostly replaced by more modern technologies like lithium-ion or nickel metal hydride (NiMH), which don’t have the “memory” problem that plagued NiCds and limited their capacity and lifetime. Second, most chargers are smarter now, limiting recharge current, sometimes delivered in pulses rather than continuously, often with automatic shut-off when it senses the battery is full or temperature is too high.

So nowadays the only overcharging you usually worry about is for the price of the equipment!

If you suspect your equipment uses cheap batteries or old technology—or if the battery becomes very warm to the touch with continued AC power—then unplug the charger.

Another aspect of your question, “Is it good to leave rechargeable things plugged in?”:

No, it’s not good for the environment, or the global energy economy, to leave dozens of small transformers attached to ac power, all of which inevitably consume standby power—however small—even when the rechargeable devices they’re connected to are already fully charged. Parasitic power, I think, is the term in vogue. We should strive to reduce parasitic power losses.

Rechargable batteries can only be charged so many times before it dies. (Probably 1000s) Whenever the battery meter is full, it takes one of those times away. However, if you leave the charger in when the battery meter is full, it will keep taking away number of charges. It’s best to take the charger out when it’s finished, for the sake of your battery and the environment too.

Lithium-ion batteries are sensitive to temperature and to exposure to oxygen. They also degrade faster if stored with a full charge, but even under the best case scenario, they lose an average of 5% of their capacity per year; more if subject to the thermal stresses of use and proximity to a warm CPU… or the thermal stress involved in charging. Under normal use, 20–35% per year is more typical.

Most LiOn chargers are smart enough to cut off the charger when the battery is full, so it’s not a terrible issue except that you have the battery at 100% charge at all times and thus degrading at least twice as fast as it would at 40% charge. There isn’t a memory effect to worry about like there is with NiCads, but LiOn batteries have their own issues.

Personally, I leave my laptop unplugged most of the time, unless I have it set to do some unattended task that will last longer than 15 minutes. I don’t want it to shut down halfway through a file transfer of an anti-virus sweep, and my Power Options are set so that it shuts down after 15 minutes of idle time when on battery power but never shuts off when plugged in. Same goes for my iPod; when the battery meter reaches 100%, I unplug it unless I am syncing it.

Either way, I don’t plan on any of my LiOn batteries lasting long. My 4-year-old Sansa used to last about 14 hours of music playback and now is closer to 6. My 1-year-old netbook went from 2:53 to 2:25 on a charge (a loss of ~16%). Batteries wear out no matter what.

@gasman There is a reason why good power supplies and chargers don’t use actual transformers to step down voltages any more. While there is stil a few milliamps flowing through a charger that isn’t currently charging, it is nowhere near what it used to be with the old-school ones. That said, last time I calculated the effects based on the chargers in my house, the difference was pretty small. I saved a lot more by switching from incandescent to CFL lights.

@jaytkay Most laptops do indeed have such a charger. However, as laptops generally get warm, especially those that are not a CULV design (basically, anything in a desktop replacement or gaming laptop as opposed to something low-powered like mine which is designed to get 8 hours on a 6-cell battery) I am not surprised. The best you could’ve hoped for was losing about half your capacity in two years, and probably closer to 70–80%.