Question about Lithium Ion Technology...?

[chazdraves]

Well, this may be an obvious question, I really don't know enough to know and I do apologize for the influx of questoins from myself.

Anyhow, for the uninitiated, I have a Galaxy Tab that I'm trying to figure out. Just the other day, my Samsung Keyboard Dock arrived and I'm thrilled with it but it has me wondering a bit more about battery technology. Specifically, I read that Lithium Ion batteries (I read this at batteryuniversity.com) are good for 300-500 cycles. In my case, I like to use the keyboard dock several times a day and I like to have it plugged into the wall while I do so that the device is always being "topped off". My question is, does each of these mini charges count as a charge cycle? That is, should I be waiting until the battery is around 50% to recharge and have the cord unplugged any other time I use the dock?.

Thanks for your time and patience!
- Chaz

 

[ChronoReverse]

Partial cycles do not count as "full cycles" for lithium ion batteries.

 

[chazdraves]

Excellent, I was really hoping someone would say that. So, is it the sort of math wherein 10 10% charges equal one full cycle or is there more to it?

 

[pm]

The math doesn't quite work like that. But if you take a lithium ion battery and never cycle it - just constantly top it off, after ~2-4 years, your battery will hold ~50% less. So the batteries wear out regardless of cycling. The concept of a cycle is that lithium ion-based cells really don't like being totally discharged. And so dropping below about 30% of capacity left is particularly costly.

Lithium ions do not like to be fully depleted but they don't want to be fully charged either. Their ideal state for longevity is around 50% capacity, and if you wanted maximum life you would reduce the total capacity of the battery and run it between ~30% and 70% of capacity (so 30% left in the battery is now "0", and 70% is now "100%"). This is how the new lithium ion based cars work - they reduce the total capacity of the battery in favor of longevity. If you can keep a lithium ion battery under 25C (86F) and use it around half capacity, it will last over 10 years. The farther you get from this ideal state the shorter it's statistical longevity vs. capacity.

Still the biggest factor to keep your battery alive as long as possible is to never let it get really hot. If you can keep the temps below 35C (95F), you will get much longer life out of the batteries than if they consistently stay above that. Beyond that, there's not much you can realistically do.

I just upgraded my car into a plug-in hybrid - I had a thread in "The Garage" forum - and added in 4kW of lithium iron phosphate batteries. I was looking at the way the balancer works on the pack and it's setting it to a max voltage of 3.3V - versus a theoretical max of 3.6V. So I interpreted that as leaving capacity on the table in order to improve longevity.

 

[CurseTheSky]

In anything with a replaceable battery, I take caution not to abuse it with heat or deep (true 0&#37 discharges, but otherwise I just use it normally. If you go into the BIOS of most laptops, you may be able to find settings to set the minimum and maximum battery levels. On my Envy 14, for example, I think the minimum (0% in Windows) is actually 7% on the battery, and maximum is something like 97%. I'd imagine phones and other electronics have similar features that are hidden from the end user.

With that said, I try to avoid situations that will prematurely degrade the battery, such as storing in a hot place, leaving it plugged in at 100% for long periods of time, letting it discharge all the way, or storing it with a very low charge for a long period of time (parasitic draw will often bring it down to zero, which means deep discharge). But the bottom line is, the battery is going to lose potential over time regardless, so I don't worry too much about it. I figure in about 2-3 years, it's time for a replacement battery or a replacement device.

 

[ChronoReverse]

Another thing to keep in mind is that lithium ion batteries degrade over time no matter what.

So in three years, even if you've very carefully used that battery, the charge it'll hold will be much less than when it's new.

 

[chazdraves]

Exactly the kind of information I hoped to find. Thanks, guys! I guess I will use it as I normally would without worrying too much. I never let it deep discharge and I don't let it get hot. 3 years would likely be acceptable to me. I wonder if the Galaxy Tab battery is replaceable?

- Chaz