First battery to recharge in less time than it discharges?
August 17, 2006 4:38 AM   Subscribe

Have batteries in consumer electronics and laptops always recharged in less time than they discharged? If not, when did it switch to being the way it is now?

To specify (or clarify, as I'm not sure I'm using the right word!), I mean discharge as the amount of time the battery lasts while being used, not in regards to any other way of quickly draining the power from it.
posted by NotMyselfRightNow to Technology (7 answers total)
Erm, this isn't an intrinsic property of a battery. The charging time may be (although it also has a lot to do with charger design), but the discharge time is entirely dependent on the drain of the thing the battery belongs to.

If there's been an improvement to the ratio, it's probably down to improvements in minimizing power consumption of portable electronics rather than changes to the batteries themselves.
posted by cillit bang at 4:46 AM on August 17, 2006

I don't know if they count as consumer electronics or not, but when I was a kid, I had one of those low-end RC cars. I loved the thing, except it took 3-4 hours to charge, and 15-20 minutes to discharge. I had 3 batteries, and I'd charge them all in tandem so I could actually get some worthwhile playtime out of the thing.
posted by god hates math at 5:26 AM on August 17, 2006


How long a battery lasts will depend a lot on what kind of load you put in it. How long a battery takes to charge will depend on the properties of the battery type, as well as performance of the charger. There certainly are batteries coming out with greater capacity, better faster chargers (for certain types of batteries) yada yada, but it'd be crazy to say that all this is coming from improvements on the battery itself.
posted by Muu at 5:50 AM on August 17, 2006

Ni-Cd batteries (as used in older standard rechargeable batteries and older laptops) would usually take longer (much longer) to charge than the rate they would normally be used at. Ni-Cd batteries were easily damaged by Ni-Cd quick-charging (often because they would easily end up overcharged), which is why quick-charging products would usually reccomend you don't use quick-charge on the batteries all the time.
posted by shepd at 6:44 AM on August 17, 2006

There is no correlation between charge and discharge times.

Your observation sounds rooted in specific devices, but is not generally applicable to all devices/batteries.

It's like asking how long it takes to empty a bucket that you filled up with a hose. The variables? Flow rate from the hose (current into the battery), size of the bucket (capacity of the battery), and method of emptying (discharge).

Kicking the bucket over empties it a lot faster than draining it through a pin hole.

Consumers prefer to have their devices charge instantly and last forever, so a lot of effort has been expended to achieve faster charging times. Most of it involves pumping as much current into the battery as it will tolerate without excessive heating and the inevitable thermally induced mechanical distortions, as well as some chemical effects. Different technologies have characteristic behaviors in this regard.
posted by FauxScot at 7:05 AM on August 17, 2006

Laptop batteries now take more time to fully charge than they do to discharge. Mine for example takes 6-12 hours to charge and only 3 hours to fully discharge.
posted by Mitheral at 7:08 AM on August 17, 2006

And, on the other hand, my Compaq evo battery will take a full charge from oh, say about 9%, while powered off, in about an hour and three quarters, and run for 3+.

It depends on two things: how much larger than the drain rate is the number of mAh between fully charged and minimum-safe-discharge voltage (my Olympus E-10 can only about about 1400-1600mAh out of my 2500mAh batteries before shutting down), and the maximum safe charge voltage of the cells (which depends on lots of things).

Discharge *rarely* depends on the current delivery rate of the battery pack (which is why LiIon packs and some cells have built in current limiters -- they *will* overheat enough to explode if they don't... as the Dell problem illustrates (and that's individual cells))...

except for RC Car packs; which tend to be 10 or 20 to 1 biased in favor of discharge, for which you want cells with the lowest internal resistance -- and matched resistances, so you don't unbalance the cells into reverse charge and failure.

Why yes, I used to work for a battery company; how did you know?
posted by baylink at 11:06 AM on August 17, 2006

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