Li-ion battery degrade?

[Bob Engelhardt]

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

 

[Phil Allison]

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

 

[Ian Field]

"Bob Engelhardt" <BobEngelhardt@comcast.net> wrote in message
newsu5pak0100q@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.

 

[Bob Engelhardt]

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

 

[default]

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.

 

[Bob Engelhardt]

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.

 

[default]

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.

 

[Bob Engelhardt]

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.

 

[default]

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)