I’m not really concerned with speed of charging or number of slots, main priority is charging in a way that prolongs battery life.
So first question: Are there any charging profiles better than CC->CV with a low-current based end of charge? My bench power supply can do that just fine, and is what I’ve been using so far.
I’m thinking maybe something like how pulsed current is sometimes used to deal with sulfation in lead-acid batteries.
Considerations I know of regarding charging and battery life are:
Charging termination voltage - anything over 4.2 V is going to start damaging the cell pretty fast. 4.1 V is a common choice is lowered capacity is acceptable, and ~3.6 V is used for long term storage.
Charging current - Samsung recommends .5C for the standard charging rate of their 35E, and .3C for longevity. I’m not sure how far this extends though.
End of charge current - Samsung lists .02C for standard charging and .03C for longevity. Besides a very long charge time, why not just do the entire charge at .02-.03C? Is there any damage that will be done by leaving 4.2 V applied to a cell indefinitely?
Any recommendations for chargers with these considerations? And what would they get me that a bench power supply wouldn’t (besides charging more than one at a time)?
Its not chargers that matters much, its charge termination voltage, charge speed and storage charge.
Charge speed is best at 0.25C or less. Meaning 1/4 of the cell capacity or less.
Most chargers charge too fast which sucks. I typically charge at 1A and no more for 18650s and 21700 and 26650.
I charge to 4V (80%-ish). Pull the cell off the charger when it gets to about 4V. Or drain in a flashlight to 4V before putting the light away.
And i store cells at 4V or less. There are a few i just fully charge but consider those batteries expendable (and still try to use the light for a bit once it comes off the charger).
I know of no charger that will terminate at 4V which is what i want.
Also its best not to drain cells, recharge before they are completely empty.
Finally if you can get cells for cheap then don’t worry too much about babying them. Here in Canada cells are hard to get without paying an arm and a leg.
4 x 21700s from Illumn plus shipping would cost me almost $100 CAD
I think you got it all and if you don’t need the convenience/simplicity of a bay charger then there’s no reason to change from doing it with your supply. Basically heat is the biggest enemy of cells, so slower charge and lower rates of discharge are the key to eking out the longest life. Anything over the nominal voltage is an overcharge anyway, but yes, if you want to pull them at 4.0v or 4.1v then you might squeeze out a few more cycles. In most lights and devices that extra top off isn’t going to do anything but be burned off as heat/inefficiency anyway (there are some applications, like some UV lights, where that extra bit of voltage can be slightly beneficial, though). All that said, and as Bort said, the differences here are pretty small and you don’t see huge gains or anything, and cells are cheap enough and easily available enough so that you can let the regular charge algorithms do their thing and not worry about it.
But if you can keep them cooler, all the better. (Also, use in deep cold temps is rough on many cells…more so when charging than discharging, and for safety reasons you absolutely want to let a cell warm to room-ish temperature before charging if it has been saturated in cold temps.)
No need for pulsing but that’s typical with NiMH. There was some very interesting research recently that investigated a pulsed charge as a way to “repair” li-ion and get more life…seemed quite effective but it was more of a petri dish experiment (literally). No idea if it would would scale up and hold practicality for actual cells with a jellyroll, but perhaps one day we’ll see charging methods use it if it can be proven as useful.
I don’t know about leaving an applied charge to fully charged cells. Li-ion of course has very low self discharge, so there is no need to do so unless it were a floating charge application like car batteries (where the lead acid benefits), but I would imagine that there is some heat involved and thus wouldn’t be smart, especially at full charge (not to mention potential risks of accidental overcharge).
If you wade through Battery University there may be some pertinent articles (more recent ones) that address these situations. A lot of this was hashed out many years ago and hasn’t really changed much but people are always still researching, testing, and learning.
The expensive Skyrc NC3000 can be configured to stop at lower voltages and have fine steps of charging current.
Lower current should be make no problems with LiIon, it just increase the time. With NiMH it could cause problems because of termination.
Some chargers have a “storage”-function which charge to 3,6V or something but it work not reliable with all chargers
Other possibility: Most chargers (except Xtar Dragon and some very cheap ones) show voltage and charged capacity, just eject the cells before charging finished
Charging between 4.1 — 4.15 / capacity loss is minimal and not draining them down below 3.3 is two of the best things you can do to prolong cell life —- Or do what I do — I buy when they’re on sale — put some in storage 3.83 — the rest I use in my lights , I charge to full and Abuse them till empty —- then Repeat
