Rechargable Li Batteries & Deterioration & Charging

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Psamathe
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Rechargable Li Batteries & Deterioration & Charging

Post by Psamathe »

I appreciate that discharge/charge cycles deteriorate the capacity of rechargeable Li-ion batteries (from memory I've see have quoted 400 cycles drops performance to 80% of new, elsewhere same for 500 cycles). Noting that a "cycle" is a complete discharge and charge so 100%->50% and charge 50%->100% is only half a cycle (approx or at least not a fulle "cycle")

Question: If you have a fairly "tired" battery (e.g. in a rechargeable LED light) e.g. running at 60% of new capacity, does it only take 60% of the power to recharge it or does it still take the full (as new) power to recharge (but just generates more heat)?

Ian
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6.5_lives_left
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Re: Rechargable Li Batteries & Deterioration & Charging

Post by 6.5_lives_left »

Psamathe wrote: 21 Sep 2021, 4:52pm Question: If you have a fairly "tired" battery (e.g. in a rechargeable LED light) e.g. running at 60% of new capacity, does it only take 60% of the power to recharge it or does it still take the full (as new) power to recharge (but just generates more heat)?
I don't know for sure but yes some of the loss of capacity will be because some of the power is being wasted as heat during discharge. Old batteries ( or cells) have a higher internal resistance than pristine cells. When the internal resistance gets too high as the cell ages, when you attempt to draw power from the cell, the high internal resistance of the cell means that power is wasted at heat in the cell instead of being delivering as power into the load.

However I am not sure that this is major mechanism for the lost of cell capacity, it might only be a secondary effect.

With lead acid cells (batteries) one of the ways that a cell can loose capacity is by bits of the plates in the cell falling off and forming a sludge at the bottom on the cell. All that material in the sludge is no longer available to "take part in the chemistry" of the cell. So the capacity of the cell goes down. Moving back to a lithium ion cell, there might be some mechanism that changes the material in the anode and/or cathode of the cell that locks the material up so that it can't take part in the chemistry of the cell, so the capacity goes down just like the lead acid cell.

Going back to the cell internal resistance. A few year back there was a big hoo-ha when Apple (electronics firm) got caught limiting the performance of older mobile phones as their batteries deteriorated. They changed the software of the older phones so that the processors ran more slowly. This was cause for lots of complaints from Apple customers. But I think it was actually a smart move by Apple. The power losses in the cell depend on the current drawn from the cell and the internal resistance , I*I*R (I squared R). R is the internal resistance of the cell. I is the current. If apple ran the processor in the phone at half the speed (MHz), the current I is halved, but the power loss in the battery is reduced by a factor of 4. This means you can keep the phone working even though it is running off a past it's best battery.
busb
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Re: Rechargable Li Batteries & Deterioration & Charging

Post by busb »

6.5_lives_left wrote: 21 Sep 2021, 9:55pm
Psamathe wrote: 21 Sep 2021, 4:52pm Question: If you have a fairly "tired" battery (e.g. in a rechargeable LED light) e.g. running at 60% of new capacity, does it only take 60% of the power to recharge it or does it still take the full (as new) power to recharge (but just generates more heat)?
I don't know for sure but yes some of the loss of capacity will be because some of the power is being wasted as heat during discharge. Old batteries ( or cells) have a higher internal resistance than pristine cells. When the internal resistance gets too high as the cell ages, when you attempt to draw power from the cell, the high internal resistance of the cell means that power is wasted at heat in the cell instead of being delivering as power into the load.
The recharging cycle on Li ion batteries is fairly complex & IIRC, starts off with a CV phase then CC then trickle. If the internal resistance increases with age, I'd suggest the charging time will take longer. A quick google seems to verify this.

It was pretty sensible of Apple to do what they did but was pretty stupid not telling people or allowing the user to choose with a setting.
Psamathe
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Re: Rechargable Li Batteries & Deterioration & Charging

Post by Psamathe »

Background to question: On my new pedal thing I'm using lights and on tour power becomes a constraint and my front rechargeable light is fine for good length rides but the battery is old and limited so I would not want to waste loads of my limited solar power/battery pack (which mostly comes from the solar cells anyway) generating heat in an old battery. e.g. a new light might take 10 units to recharge after a ride and if the old one would take 20 units charge for the same use then that could become an issue with limited power. But is old only took same recharge power as new after same use then as long as it lasts a ride then no problem.

Ian
xerxes
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Re: Rechargable Li Batteries & Deterioration & Charging

Post by xerxes »

6.5_lives_left wrote: 21 Sep 2021, 9:55pm
Psamathe wrote: 21 Sep 2021, 4:52pm Question: If you have a fairly "tired" battery (e.g. in a rechargeable LED light) e.g. running at 60% of new capacity, does it only take 60% of the power to recharge it or does it still take the full (as new) power to recharge (but just generates more heat)?
I don't know for sure but yes some of the loss of capacity will be because some of the power is being wasted as heat during discharge.
The OP is asking about the power required to recharge the battery.
PH
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Re: Rechargable Li Batteries & Deterioration & Charging

Post by PH »

xerxes wrote: 22 Sep 2021, 3:46pm
6.5_lives_left wrote: 21 Sep 2021, 9:55pm I don't know for sure but yes some of the loss of capacity will be because some of the power is being wasted as heat during discharge.
The OP is asking about the power required to recharge the battery.
It's the same question.
Doesn't matter where it's lost the question is how much light for X amount of charging, whether it's a loss from the powerbank that doesn't add to the batteries capacity, or a loss in the batteries ability to run the light, for the scenario of the OP it amounts to the same thing.
I'm not an expert, but have a fair bit of experience with power tool batteries, they still take the same amount of charging even when the capacity drops.
Add to that, if you're trying to maximise the light run time available from a powerbank, you might also consider that the tech is improving, the LED light I have now is considerably more efficient than the one I've had for about seven years. I kept the older one with the intention of using it within it's capacity for shorter rides, but really the difference is such that it's just gathering dust.
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