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Li-ion batteries are not “trickle charged”

Zoomit

Active Member
Sep 1, 2015
2,245
4,275
SoCal
I often see those in this forum and across the EV community use the term “trickle charging” to indicate an especially slow charge rate, such as 1 kW AC Level 1 charging. That’s misappropriating the term. To quote Wikipedia, “trickle charging means charging a fully charged battery at a rate equal to its self-discharge rate, thus enabling the battery to remain at its fully charged level.” Lead-acid batteries are commonly trickle charged when stored. It continues:

“Other battery chemistries, such as lithium-ion battery technology, cannot be safely trickle charged. In that case, supervisory circuits (sometimes called battery management systems) adjust electrical conditions during charging to match the requirements of the battery chemistry. For Li-ion batteries generally, and for some variants especially, failure to accommodate the limitations of the chemistry and electro-chemistry of a cell, with regard to trickle charging after reaching a fully charged state, can lead to overheating and, possibly to fire or explosion.”
I realize this is pedantic, but trickle charging has a very specific meaning with a well defined purpose. No one is trickle charging their Li-ion EV battery.
 

Valore

Member
Apr 26, 2018
401
450
Florence, Italy
Lithium batteries are using CC-CV charging.
So first constant current (CC) until 4.2V per cell (or whatever the BMS allows) is reached, then constant voltage (CV) until charge current is down to like 10% of initial current while keeping the maximum voltage. Then they're considered fully charged.
This is why the charge rate "goes down" when the battery has more charge and peak charge rates are reached only at lower SOC.
With large packs like in cars there is also a balance charge phase, concurrent or after CV phase where the BMS is equalizing all cell cluster that are in series.
This balancing phase can take quite a long time and draw some current, what some people might confuse with "trickle charging".
 
Last edited:

cwerdna

Active Member
Jul 11, 2012
3,638
2,546
SF Bay Area, CA
I often see those in this forum and across the EV community use the term “trickle charging” to indicate an especially slow charge rate, such as 1 kW AC Level 1 charging. That’s misappropriating the term..
Unfortunately (?), some automakers specifically use the term "trickle" charge to refer to L1 charging.

Here's page CH-5 from the '15 Leaf manual. You can d/l it from https://www.nissanusa.com/content/d...s/leaf/2015/2015-Nissan-LEAF-owner-manual.pdf.

IIRC, Nissan has used this terminology since 1st model year of Leaf (2011) and I believe continues to do so (it's still that way in the '19 Leaf manual). '11 to '17 US market Leafs from the factory only shipped with an L1 120 volt 12 amp EVSE, for 1.44 kW at max.
 

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Zoomit

Active Member
Sep 1, 2015
2,245
4,275
SoCal
Lithium batteries are using CC-CV charging.
So first constant current (CC) until 4.2V per cell (or whatever the BMS allows) is reached, then constant voltage (CV) until charge current is down to like 10% of initial current while keeping the maximum voltage. Then they're considered fully charged.
This is why the charge rate "goes down" when the battery has more charge and peak charge rates are reached only at lower SOC.
With large packs like in cars there is also a balance charge phase, concurrent or after CV phase where the BMS is equalizing all cell cluster that are in series.
This balancing phase can take quite a long time and draw some current, what some people might confuse with "trickle charging".
Tesla doesn’t use a typical CC/CV charge profile. I would describe it as a constant power phase then a near constant voltage phase at 400V.

I would like to hear if you know differently, but it’s my understanding that the Tesla packs, or at least the Model 3/Y packs, have no means of isolating individual bricks that would be needed for a “balance phase” during charging. I know they add a bleed resistor to pull down high bricks when the pack is in stand by or asleep. The section of the Service Manual is available in this post for more details on brick balancing via the bleed resistor.

Battery Management System - What I Learned At Tesla Service Center
 

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