Battery Musing: Does charging our batteries slowly lead to a more complete charge? -- Part 2

[Mooch]

I screwed up!
When I posted earlier about this topic I was only discussing chargers that had a fixed current cutoff to know when to stop the charge. I had forgotten that vapers are starting to use the "hobby" chargers favored by the radio-control communities.

Some of these chargers have a "C/10" current cutoff. The cutoff isn't fixed, it's often set to 1/10th of the charging current setting. For example, if you are charging at 1A the charge will stop when the current drops to 0.1A.

Will using these chargers mean that charging slowly will lead to a more complete charge?

Bottom line: Yes. The battery's capacity does increase at lower charge rates, but it does so only by a small amount. Charging at 0.5A increased the capacity by about 1.8% versus charging at 2A.

Additional Information: I charged a Samsung 25R at four different rates, from 0.5A to 4A, and then discharged it at 5A each time. As you can see in the graph below, the capacity the battery delivered down to 2.5V changed by up to 3.2% across all four discharges. This is a lot more than the 0.25% change in capacity when using chargers with a fixed charging cutoff current.



For more reasonable charge rates, 0.5A - 2A, the capacity of the battery increased by about 1.8% when charging at 0.5A instead of 2A.

My apologies for the confusion and for dividing this topic into two posts!

Part1:
Battery Musing: Does charging your batteries slowly lead to a more complete charge?

 

[DaveP]

Good post, Mooch.

Lithium batteries are a mystery that we all want to understand. Do we charge until it gets really warm or do we take it off as soon as it hits 4.2v? If it's a little warm is that bad? Should we let it sit in the charger until the LED turns green? Should we slow charge at .5A or let it rip at 1A so we can vape on it sooner? What about charging an 18650 when we are going to store it for backup?

I've always thought that slow is better. Heat is the enemy of all batteries. If I won't need it until tomorrow and I'll be around to baby sit the charger, I like .5A. If I have two married sets and one is already down to about 20%, I want the backup charged quicker.

My LUC 4 charger can do 2A, but that's supposed to be for larger cells, like 26650, isn't it? My 18650's get warm at 1A charge rates and stay cool at .5A. If heat is the enemy, then I'd think that .5A is the best charge rate.

 

[sofarsogood]

My understanding is both charging and discharging reduce battery endurance over time (charge cycles) and the decline over time is slower if a battery is charged or recharged at lower rates. If I'm right about that it's beneficial to charge and recharge at lower rates. Anyone feel free to correct me if that's not accurate.

 

[Mooch]

Good post, Mooch.

Lithium batteries are a mystery that we all want to understand. Do we charge until it gets really warm or do we take it off as soon as it hits 4.2v? If it's a little warm is that bad? Should we let it sit in the charger until the LED turns green? Should we slow charge at .5A or let it rip at 1A so we can vape on it sooner? What about charging an 18650 when we are going to store it for backup?

I've always thought that slow is better. Heat is the enemy of all batteries. If I won't need it until tomorrow and I'll be around to baby sit the charger, I like .5A. If I have two married sets and one is already down to about 20%, I want the backup charged quicker.

My LUC 4 charger can do 2A, but that's supposed to be for larger cells, like 26650, isn't it? My 18650's get warm at 1A charge rates and stay cool at .5A. If heat is the enemy, then I'd think that .5A is the best charge rate.

Slower is better but most of our batteries can easily take 1A without noticably affecting overall battery life. When being charge it spends very little time being warm.

2A charging is definitely not better for 26650's as their internal resistance is higher than 18650's. 1A recommended, 2A max.

Charge until the charger says it's done.

When storing batteries you should discharge them down to about 50%.

 

[Fozzy71]

...
When storing batteries you should discharge them down to about 50%.

How would you go about discharging them without using them in a mod? Can my efest 6 bay charger discharge them somehow?

I bought 18 new batteries for married sets in my 4 new triple battery mods and charged all of them once I got them but stored 2 of the mods after testing them, and have only been rotating 4 sets of 3 in the 2 mods I am using. I didn't know you shouldn't fully charge them for storage. Or maybe I should just forget about using these 6 batteries as married sets and put them into rotation for all of my single battery mods?

 

[Mooch]

How would you go about discharging them without using them in a mod? Can my efest 6 bay charger discharge them somehow?

I bought 18 new batteries for married sets in my 4 new triple battery mods and charged all of them once I got them but stored 2 of the mods after testing them, and have only been rotating 4 sets of 3 in the 2 mods I am using. I didn't know you shouldn't fully charge them for storage. Or maybe I should just forget about using these 6 batteries as married sets and put them into rotation for all of my single battery mods?

Efest chargers don't have a discharge function. Using your mod is, by far, the best way to bring your batteies down to about 50% in preparation for storage. I recommend just rotating through all your sets though. Batteries are still aging when in storage and you need to occasionally bring their voltages back up by charging them a litle. It's a lot easier to just rotate through all of them.

You can certainly use those six in single battery mods too.

 

[Fozzy71]

thanks for the reply @Mooch