best charge + storage practices for 18650's (samsung 29E)

[fly76]

hi.

i've been looking through this forum a bit as well as others to try to find out how to get the most life from my ebike battery pack. if anyone has any advice or can point me to another thread that already answers this then great, thanks. i'm assuming that most 'best practice' ideas will apply equally to my 29E cells as to all Li-ion 18650's.

my set up is 37V 10S 4P pack of 18650's powering an old Heinzmann classic hub and controller and i have a 2A charger. it appears that the high drain of this old motor and controller (its rated at 30A max continuous) is already a factor that will reduce the life of my pack .... so just trying to give it all the help i can...

question's
1 - what is the best voltage to discharge down to? is the 2.8V cut out of the BMS too low for repeated discharges?
(i usually don't take it down past 34/35V ie 3.4/3.5V per cell assuming they are all balanced)

2 - i have read that batteries should not be charged for 90 mins of being discharged. would this be to allow them to cool before applying current to them? any truth behind this as the charge current is way below any discharge rate?

3 - as li-ion's are best stored long term at around 50% rather than at 100%, does it also hold true that i should not fully charge the pack (ideally) until i am about to next use it? this would allow the pack to remain most of its life in a discharged state. if i always charged as soon as i arrive back it would spend most of its time fully charged even if it was only for 1-4 days between any amount of discharge...

4 - should i always remove the battery pack from the bike and bring it into the house to reduce the effects of fluctuating storage temperatures int he un-insulated garage where the bike is kept? ( i don't do this at the moment as it is summer here in the UK. the most extreme temps would usually be between -5C to + 30C)

thanks

 

[Cephalotus]

1 - what is the best voltage to discharge down to? is the 2.8V cut out of the BMS too low for repeated discharges?
(i usually don't take it down past 34/35V ie 3.4/3.5V per cell assuming they are all balanced)

I would store them above 3.0V, this includes discharge from BMS during storage

2 - i have read that batteries should not be charged for 90 mins of being discharged. would this be to allow them to cool before applying current to them? any truth behind this as the charge current is way below any discharge rate?

I see no problem as the cells are not very hot. Otherwise regen would kill a battery.

Avoid quick charging below 10°C, avoid charge below 0°C if possible.

3 - as li-ion's are best stored long term at around 50% rather than at 100%, does it also hold true that i should not fully charge the pack (ideally) until i am about to next use it? this would allow the pack to remain most of its life in a discharged state. if i always charged as soon as i arrive back it would spend most of its time fully charged even if it was only for 1-4 days between any amount of discharge...

yes.

4 - should i always remove the battery pack from the bike and bring it into the house to reduce the effects of fluctuating storage temperatures int he un-insulated garage where the bike is kept? ( i don't do this at the moment as it is summer here in the UK. the most extreme temps would usually be between -5C to + 30C)

For long time storage I keep them in the fridge at 5°C (with a dry pack) at low to very low charge levels. Give them some time to warm up before charging or avoid quick charging when cold.

For normal use daily or every few days I just try avoid very cold temperatures and heat. 15°C would be nice, 10°C or 20°C will do, too. 25°C is fine, too, but cells will degrade a bit faster.

If you can live with a lifetime of maybe 2-3 years this is not very important, if you want a lifetime of 10-15 years keeping them well will help.

Avoid heat! Don't put a black fully charged battery for hours into the summer sun cooking at 60°C.

 

[fly76]

thanks Cephalotus for the ideas and info as well as confirming some of my thoughts. i'm using the battery fairly regularly so i guess it will be past its best in a a few years so not expecting to get 10-15 out of it...

though for now i have something else to work out with the pack... the battery died on me while out riding for only the second time and it looks like that the cut off is only at 3.3V not 2.8V that i had been told for this BMS. this doesn't make sense to me given the BMS specs and also obviously reduces my range quite a bit. the motor was struggling relatively for the last KM, only giving me about 14mph rather than the usual 17-19mph. like i said before i never normally take it down below 3.4V per cell, but always thought that i had a fair bit in reserve. could there be an individual cell or two that is at a lower voltage and causing the pack to cut out?