Lithium batteries "memory"

[Murflynn]

I read everywhere on the web that one of the advantages of lithium batteries is that they do not have a "memory" whilst NiCads do.

 

I have an EPropulsion 1.0 outboard with a 1.3kwh 40v battery in my boat which is moored at the back of my home.  I go for frequent short trips and I used to connect the charger each time I returned, and disconnect it when the indicator light went blue.  When I went for a longer trip the battery charging indicator gradually dropped from 95% to 80% and then plummeted to 15%.  Soon after the system shut down for "low battery" .

 

I took the battery  to EPropulsion's depot in Hamble and the technician checked it out.  All the cells were healthy.  He advised me not to charge it each time I use it, but to run it down to about 20% before charging in order to keep the  cells in balance.  Luckily I have a spare battery so this is manageable.  The user manual simply states to avoid overcharging and makes no reference to cycling the battery over a wide range.

 

Perhaps someone could explain why this situation is not effectively the same thing as a "memory" issue.

[Chewbacka]

My understanding is for best life is to keep a lithium battery between 20~80% and not to store it fully charged.  

[nicknorman]

1 hour ago, Murflynn said:

I read everywhere on the web that one of the advantages of lithium batteries is that they do not have a "memory" whilst NiCads do.

 

I have an EPropulsion 1.0 outboard with a 1.3kwh 40v battery in my boat which is moored at the back of my home.  I go for frequent short trips and I used to connect the charger each time I returned, and disconnect it when the indicator light went blue.  When I went for a longer trip the battery charging indicator gradually dropped from 95% to 80% and then plummeted to 15%.  Soon after the system shut down for "low battery" .

 

I took the battery  to EPropulsion's depot in Hamble and the technician checked it out.  All the cells were healthy.  He advised me not to charge it each time I use it, but to run it down to about 20% before charging in order to keep the  cells in balance.  Luckily I have a spare battery so this is manageable.  The user manual simply states to avoid overcharging and makes no reference to cycling the battery over a wide range.

 

Perhaps someone could explain why this situation is not effectively the same thing as a "memory" issue.

LiFePO4 batteries do suffer from a memory effect but it is quite reversible. After say 6 months of being in a mid state of charge, capacity is reduced. Keeping the batteries in a mid state of charge is still the best idea for max life, but every 6 months or so one should fully cycle the battery to recover the lost capacity, if having max capacity available is important to you.

 

In your case it does seem rather extreme, but you are presuming that the charging function and the BMS’ SoC are doing their jobs properly, which may not necessarily be the case.

 

eg this text

”It is strongly recommended to store lithium batteries indoors during the off-season. It is also recommended to store LiFePO4 batteries at a state of charge (SOC) of approximately 50% or higher. If the battery is stored for a long time, cycle the battery at least once every 6 months. Do not store discharged batteries.”

 

from here: https://explorevanx.com/blog/how-to-store-lifepo4-12v-batteries

 

 

Edited September 14, 2022 by nicknorman

[Murflynn]

thank you Nick.    it confirms more or less what I thought - a pity the very well-written owner's manual wasn't checked by the technicians in the front line who have to deal with customers.

 

just for the record, the EProp motors are fantastic and, according to all the reviews, a step ahead of Torqeedo which were the gold standard but are now having to play catch up to match EProp.