# Why is there a maximum charging current much lower than maximum discharging current on a li-ion pack?

I will have soon an electric scooter with a 60v (top 67.2v) and 35ah battery pack. As it is designed, it can be charged by one charger which pumps 2,5 amps or it can be charged by 2 chargers in parallel, pumping 5A. That's ok for city use, it can charge over night, there is no problem waiting few hours for a full charge. But from time to time I plan to take trips into forest, between villages, etc. and I may need to charge it on my way, much faster, in an hour or so. For that I can purchase a 60V and adjustable 5-25A charger to take with me and plug it where I can find a wall plug, then continue my trip. But searching on aliexpress for similar sized battery packs, I discovered something strange in the specifications. For a 60v 20ah pack, the maximum continuous discharge current can be as high as 50 amps, but the charge current is max 5A. Why?? The connections between cells clearly can support high currents, otherwise it cannot discharge with 50A without damage. Why is the charging max so low and what happens if I push 25A with a powerful charger? Thank you.

• The cells themselves can't handle the higher current. If you push 25A through with a powerful charger, you'll probably end up with your battery catching fire. Jan 17, 2019 at 17:46
• Are you sure? How can it handle high current when discharging but not when charging? A 60v pack is made with 16 series of 3.7v li-ion cells, in my case all are 18650 format. One cell, depending on its manufacturer/model, etc can have capacity around 2-3 ah or so. Afaik, there is no problem to charge one cell of li-ion or discharge at 1C. To achieve 20ah, each 3.7v stage must have around 10 cells in parralel, thus handling 20 ah without problem, that's 1C for them. So why a pack of 16s10p cannot handle more than 5a when charging but can handle 50 when discharging? Jan 17, 2019 at 18:22
• I just looked at a random 18650, 3ah element from TME. It can be charged with 5A, that's 1.6C and discharged with 15A, that's 5C. By these figures, a 60v 20ah pack should withstand 30a charging current. But by specification, it can be charged only with 5a, that is 0.25C. Jan 17, 2019 at 18:24
• This is a good question. Did you try any academic research articles on this subject? What did you find? Jan 17, 2019 at 20:33
• I am still digging for information. I have some hints from here and there so far. Every battery pack have a BMS which, in its simplest form must provide some protection for overcharging and overdischarging as well as cell balancing. Due to cost reasons, I assume that almost all of them are using passive balancing and I think the low maximum charge current has something to do with the power dissipated on the balancing resistors, rather than with the cell itself. But I do not have a clear picture yet, still digging. Jan 17, 2019 at 20:45