# Does battery life decrease as current increases?

I'm shopping for a battery-powered USB charger.

Someone on Amazon says that as current (amperes) increases, battery life decreases exponentially. He says that using a charger with a current of 500mA gets you 30% more total power from the AA batteries than if you used a charger with a current of 1 amp.

Is this true or false?

dlgoff
Gold Member
Drakkith
Staff Emeritus
There's some confusion here. First, I assume you're talking about a lithium-ion battery since your talking about a USB charger. If not, please say so, as different batteries behave differently. Also, battery life can mean the number of cycles the battery can last through, or it can mean the amount of time the battery can be used after charging. Which one are you talking about?

I'm shopping for a battery-powered USB charger.

Someone on Amazon says that as current (amperes) increases, battery life decreases exponentially. He says that using a charger with a current of 500mA gets you 30% more total power from the AA batteries than if you used a charger with a current of 1 amp.
First claim isn't correct. Slow charging is generally better for the lifetime, but if with faster charging lifetime decreases exponentially, than it is one shitty kind of battery.

What matters most is how much voltage you push on it when it is nearly full. If you charge it at a higher voltage, it will fill faster, but will get more damage if you leave it on and it is not a smart charger. The lower voltage will fill slower, but won't damage as much in the final phase. Ideally, you want more voltage to start, and then drop it to less voltage near the end of the charge. In fact, if you don't fill the battery all the way, you will get more cycles out of it.

And if you give it the higher current faster charge and push the battery to its limit, will last longer between recharges, but it will be good for fewer recharges.

sophiecentaur
Gold Member
I really have doubts about whether PF should even be prepared to discuss battery chargers. In many ways, they are in the same class of discussion as bomb making and tasers. So many people seem to want to tackle making a battery charger as if it's the easiest part of Electronics. In fact it's very sophisticated and potentially very dangerous.

dlgoff
Averagesupernova
Gold Member
It really depends on the type of battery, sophie. I would never ever recommend a beginner to tackle a lithium ion charger. A simple approach to learning about battery charging is to charge a lead acid or NiCad battery with a lab type power supply. Use a fuse as a fail safe and dial the current and voltage around. You will learn that you really cannot change one without the other.

meBigGuy
Gold Member
Hmmmm I misread the original post.

The capacity of a battery depends on how fast you draw power from it. The ma-hours measurement is a a certain current draw. If you draw current at a higher rate, then you not only get less hours, but the ma-hours available also decrease because of battery chemistry issues.

For example:

dlgoff
Gold Member
There is no "sophie bomb" lurking in the netherlands of USB chargers.
I understand and agree that Lithium-ion Satety Concerns aren't too much of an issue.

... the lithium-ion system is safe, providing certain precautions are met when charging and discharging. Today, lithium-ion is one of the most successful and safe battery chemistries available.

But I also understand and agree that

So many people seem to want to tackle making a battery charger as if it's the easiest part of Electronics. In fact it's very sophisticated and potentially very dangerous.

And since there may be many viewers of this thread in the future who know nothing of the chemistry ...

meBigGuy
Gold Member
hmmmm --- I deleted the post with the "sophie bomb" comment when I re-read the OP. I guess you got it during the short time it was available.
There is a "sophie-bomb" lurking in any home-built (and some commercial) Li-ion battery charger, especially if not using a controller IC. It is a tricky technology.

But, to answer the original post again,

Given a commercial battery operated USB charger, the amount of charge (capacity) is affected significantly by the current draw, as the curves show for lithium ion. There are similar curves for NiMH, nicad, and alkaline batteries.

The following curves are for alkaline primary (non rechargable) cells.
http://www.powerstream.com/AA-tests.htm

sophiecentaur
Gold Member
It really depends on the type of battery, sophie. I would never ever recommend a beginner to tackle a lithium ion charger. A simple approach to learning about battery charging is to charge a lead acid or NiCad battery with a lab type power supply. Use a fuse as a fail safe and dial the current and voltage around. You will learn that you really cannot change one without the other.

Having just read the following, my opinion is much the same as it was. (In this thread)
"I need 20 or 22g wire to be completely safe at 3A, assuming I want to the transformer to not melt. I don't think I'll get all the windings of a normal transformer. Do I really need a ton of windings, or just the right ratio on each side? Will more windings be more efficient? I'm not making a super strong electromagnet. I'm just trying to change the voltage. I wonder if 120 wraps and 40 wraps is good enough. Or 60 and 20. Winding takes time."

I think I would trust the very cheapest and cheerfullest 'Far East' sourced charger than one that was constructed on the basis of this level of knowledge. "Winding takes time" haha AND SKILL!. But did the poster ever dis- and re- assemble a real transformer or look at the price of new transformer kits, I wonder?

PS, where will your average person get hold of a 'Lab type Power Supply'?

Averagesupernova
Gold Member
Having just read the following, my opinion is much the same as it was. (In this thread)
"I need 20 or 22g wire to be completely safe at 3A, assuming I want to the transformer to not melt. I don't think I'll get all the windings of a normal transformer. Do I really need a ton of windings, or just the right ratio on each side? Will more windings be more efficient? I'm not making a super strong electromagnet. I'm just trying to change the voltage. I wonder if 120 wraps and 40 wraps is good enough. Or 60 and 20. Winding takes time."

I think I would trust the very cheapest and cheerfullest 'Far East' sourced charger than one that was constructed on the basis of this level of knowledge. "Winding takes time" haha AND SKILL!. But did the poster ever dis- and re- assemble a real transformer or look at the price of new transformer kits, I wonder?

PS, where will your average person get hold of a 'Lab type Power Supply'?

You cannot be serious about one getting their hands on a lab-type supply are you?
http://www.mouser.com/ProductDetail/BK-Precision/9110/?qs=sGAEpiMZZMtd%252b2RMOh0LyzYSj8rPJe%2fBlY14bS5WKwA%3d [Broken]
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Anyone who is not willing to spend that money is not serious about electronics. There are less expensive supplies that will do the same on Mouser. I will admit the OP seems quite green. Just saying "Don't do it" will not deter most people. Here is an alternative.

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russ_watters
Mentor
You cannot be serious about one getting their hands on a lab-type supply are you?
http://www.mouser.com/ProductDetail/BK-Precision/9110/?qs=sGAEpiMZZMtd%252b2RMOh0LyzYSj8rPJe%2fBlY14bS5WKwA%3d [Broken]
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Anyone who is not willing to spend that money is not serious about electronics.
I think you are arguing against your point!

I'm actually playing around with a Peltier device and trying to decide if I need a lab quality PSU...

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Averagesupernova