Li-ion battery degrade?

Started by Bob Engelhardt November 10, 2017
I was measuring torque required to drive various drill bits and 
incidentally found that my cordless drill was delivering way less torque 
than it was spec'd for.  80in-lbs measured vs 250 spec'd.  If this 
wasn't a Milwaukee drill, I would have dismissed it as a spooky torque 
spec.  But 80 vs 250 for a Milwaukee doesn't figure.

The thought that came to me was maybe the battery couldn't deliver the 
current required for full torque.  I tried 2 batteries, fully charged, 
and the results were the same.   The batteries are 4-1/2 years old, but 
have only seen homeowner use, maybe a bit more.

So, my question is: do Li-ion batteries lose their current-delivery 
capacity with age?  Note that I am NOT talking about capacity in its 
normal sense of amp-hours, but peak current.

Thanks,
Bob
Bob Engelhardt wrote:
> > I was measuring torque required to drive various drill bits and > incidentally found that my cordless drill was delivering way less torque > than it was spec'd for. 80in-lbs measured vs 250 spec'd. If this > wasn't a Milwaukee drill, I would have dismissed it as a spooky torque > spec. But 80 vs 250 for a Milwaukee doesn't figure. > > The thought that came to me was maybe the battery couldn't deliver the > current required for full torque. >> > So, my question is: do Li-ion batteries lose their current-delivery > capacity with age? Note that I am NOT talking about capacity in its > normal sense of amp-hours, but peak current. >
** The internal impedance may rise with age causing the pack's voltage to drop significantly under load. I imagine the maker's torque spec is taken with the drill fully stalled and with full setting on the trigger. .... Phil

"Bob Engelhardt" <BobEngelhardt@comcast.net> wrote in message 
news:ou5pak0100q@news3.newsguy.com...
> I was measuring torque required to drive various drill bits and > incidentally found that my cordless drill was delivering way less torque > than it was spec'd for. 80in-lbs measured vs 250 spec'd. If this wasn't > a Milwaukee drill, I would have dismissed it as a spooky torque spec. But > 80 vs 250 for a Milwaukee doesn't figure. > > The thought that came to me was maybe the battery couldn't deliver the > current required for full torque. I tried 2 batteries, fully charged, and > the results were the same. The batteries are 4-1/2 years old, but have > only seen homeowner use, maybe a bit more. > > So, my question is: do Li-ion batteries lose their current-delivery > capacity with age? Note that I am NOT talking about capacity in its > normal sense of amp-hours, but peak current.
Rechargeable lithium cells have a finite life span whether you use them or not. Lithium primary cells can have a shelf life up to 10yrs - I think the secondary cells are somewhat less.
My post was about torque & current, but I got to wondering about 
capacity degradation.  So I built a capacity tester and got the following:

12v (2 batteries, 5 & 7 years old): 11+wh versus 14wh spec - 21% loss. 
They got quite a bit of use at home, apt building, and Habitat.

sm 18v battery, 6+ years old: 19+wh vs 23wh spec - 16% loss

lg 18v, 6+ years old: 40+wh versus 54 spec - 25% loss

These batteries are spec'ed in watt-hours instead of the usual Ah and 
watt-hours are trickier to measure.  I got the Ah easily enough and 
assumed a straight-line voltage drop, to 3v/cell cutoff that I used in 
my tester.

As an aside - I measured the peak current on one of the 12v batteries 
and got 23A.  But peak current isn't spec'ed, so I don't know what the 
loss is.

Bob
On Mon, 01 Jan 2018 10:57:52 -0500, Bob Engelhardt
<BobEngelhardt@comcast.net> wrote:

>My post was about torque & current, but I got to wondering about >capacity degradation. So I built a capacity tester and got the following: > >12v (2 batteries, 5 & 7 years old): 11+wh versus 14wh spec - 21% loss. >They got quite a bit of use at home, apt building, and Habitat. > >sm 18v battery, 6+ years old: 19+wh vs 23wh spec - 16% loss > >lg 18v, 6+ years old: 40+wh versus 54 spec - 25% loss > >These batteries are spec'ed in watt-hours instead of the usual Ah and >watt-hours are trickier to measure. I got the Ah easily enough and >assumed a straight-line voltage drop, to 3v/cell cutoff that I used in >my tester. > >As an aside - I measured the peak current on one of the 12v batteries >and got 23A. But peak current isn't spec'ed, so I don't know what the >loss is. > >Bob
Not to start an argument, but instead of peak amps, peak power would seem to be a better benchmark. With batteries, discharge rate affects capacity.
On 1/2/2018 2:15 PM, default wrote:
> Not to start an argument, but instead of peak amps, peak power would > seem to be a better benchmark. > > With batteries, discharge rate affects capacity. >
No argument here - my comment about current had to do with my original post & my wondering if batteries lost peak current capability.
On Tue, 02 Jan 2018 17:15:55 -0500, Bob Engelhardt
<BobEngelhardt@comcast.net> wrote:

>On 1/2/2018 2:15 PM, default wrote: >> Not to start an argument, but instead of peak amps, peak power would >> seem to be a better benchmark. >> >> With batteries, discharge rate affects capacity. >> > >No argument here - my comment about current had to do with my original >post & my wondering if batteries lost peak current capability.
Well, they must. The internal resistance rises with age, so the short circuit current would have to decrease.
On 1/3/2018 10:19 AM, default wrote:
> On Tue, 02 Jan 2018 17:15:55 -0500, Bob Engelhardt >> No argument here - my comment about current had to do with my original >> post & my wondering if batteries lost peak current capability.
> > Well, they must. The internal resistance rises with age, so the short > circuit current would have to decrease. >
Sure, but how much. Looping back 4 posts, I said that I measured its current current, but its initial value wasn't spec'ed. I.e., I couldn't know how much I'd lost & consequently how much peak torque I had lost.
On Thu, 04 Jan 2018 10:00:42 -0500, Bob Engelhardt
<BobEngelhardt@comcast.net> wrote:

>On 1/3/2018 10:19 AM, default wrote: >> On Tue, 02 Jan 2018 17:15:55 -0500, Bob Engelhardt >>> No argument here - my comment about current had to do with my original >>> post & my wondering if batteries lost peak current capability. > >> >> Well, they must. The internal resistance rises with age, so the short >> circuit current would have to decrease. >> > >Sure, but how much. Looping back 4 posts, I said that I measured its >current current, but its initial value wasn't spec'ed. I.e., I couldn't >know how much I'd lost & consequently how much peak torque I had lost.
I built a little AA - AAA tester with a pair of analog quartz clocks with selectable dummy loads, and battery holders mounted on a piece of wood. Power until the clocks stop. (not very scientific, but adequate for comparing batteries if I keep an eye on it) I've since gotten an "advanced" Panasonic charger for the batteries. It simply refuses to charge batteries that have a high internal resistance. I can charge them on a low tech charger and they do store some energy but peak current and maximum power point (I actually tried to measure it) both indicate the internal resistance is way up on the ones the Panasonic charger determines are "bad" and not worth charging. It also refuses to charge shorted batteries, so it seems like there's some "sweet spot" that makes it happy. I haven't tried to charge a variable resistor with a cap across it, and that would probably shed some light as to what constitutes a battery it considers worth charging. Max power transfer: source impedance is equal to load impedance But my tinkering does support the idea that a cheap and dirty way of measuring battery life may be the peak short-circuit current. (assuming that doesn't destroy the battery under test)