This is part two of a two-part post.
Manufacturer’s Current Ratings
These are for li-ion round cells still in their original manufacturer’s wrap. Not just Samsung, Sony, Murata, LG, Sanyo, Panasonic, and Molicel but the large China manufacturers like BAK, EVE, CATL, Lishen, and others too.
There is usually just one rating, a true continuous current rating that gives you acceptable performance and cycle life. For the ultra-high capacity cells (>3000mAh 18650 or >4200mAh 21700) you can definitely get better performance and less voltage sag though by not going over about 50%-75% of the rating.
But there are some cells that are rated for the applications they were designed for, hard non-continuous use. Molicels are rated this way. Their current ratings cannot be used as true continuous current ratings to compare against other cells. This is not a false rating! It is the type of rating that best helps Moli’s customers judge whether the cell might be a good choice.
There’s no way for us to know this though so we are forced to check for third-party test results that can help us judge a manufacturer’s ratings. None of the round cells we use were made for individual use by end customers so this is the situation we must deal with. The datasheets and the ratings are only for the huge commercial customers for these cells.
Murata’s VTC cells (made by Sony up until 2017) also have non-continuous ratings, allowing use up to a certain temperature. But they also have a true continuous current rating you can use to compare the cells to others.
For example…
The VTC6 is rated at 15A continuous and 30A non-continuous by Murata. But if you want to compare the VTC6 to any other cell, perhaps the Samsung 30Q, then you would have to use the continuous 15A rating. You cannot say that the VTC6 has a 30A rating and blows away the 15A-rated Samsung 30Q. They are both 15A cells and perform very close to each other (30Q slightly better in my testing).
The VTC6 has huge voltage sag at 30A anyway and these non-continuous ratings are best ignored if performance is your priority.
Rewrapped Cell Current Ratings
In my opinion, “rewrapped” cells are those that have had their original factory wraps removed (or were purchased without wraps) and have been rewrapped by a company that will resell them. This is how companies like Efest, Imren, MXJO, Vapcell, and dozens of others started out.
This was originally done with cells from Samsung, Sony, Murata, LG, Sanyo, Panasonic, and Molicel but is now also being done with cells from the large China manufacturers like BAK, EVE, CATL, Lishen, and others.
The problem is that an unscrupulous company can exaggerate the manufacturer’s rating or even create their own useless “max” or “pulse” rating. The situation has gotten a lot better lately though in the US and EU, with the rewrapping companies giving their cell more accurate ratings. Some brands like Epoch, Fogstar, and others have always had accurate ratings. In Asia though the ratings on many of the rewrapped cells are ridiculously exaggerated.
There’s no way to know if the ratings on the wrap are accurate or not unless you know what cell they have rewrapped (for cells from the large manufacturers) or have seen test results.
Any “max” or “pulse” ratings can be ignored though in my opinion. I know that these are the ratings we love to see. They are ones that are listed by most vendors and they are high. But they are, at best, just the cell manufacturer’s non-continuous rating. If not then we have no idea what criteria the rewrapper used to set the rating. At worst they are merely numbers chosen during a marketing lunch meeting.
I have had multiple rewrapping companies tell me they just make up these “max” or “pulse” numbers to please the distributors who will not buy cells unless they have a big number on them. These numbers are useless marketing bullsh*t.
Some companies rewrap very good cells so don’t think that they are all to be avoided. Vapcell has gotten a couple batches of some great cells from the big manufacturers over the last couple of years and rewrap other good cells. Just stick with the continuous current rating.
As mentioned earlier, there are also great rewrapped cells from Fogstar, Epoch, and other companies.
As the cells from the big manufacturers are getting harder and harder to find (no one buys direct from the manufacturer) the rewrapped cells from the big manufacturers are becoming a smaller and smaller part of what these rewrapping companies can offer.
Many of their cells are now coming from the smaller China factories and some are pretty good. For example, the Yong De Li New Energy Corp.’s 1000mAh 18350 that at least three companies have rewrapped.
Some of us would never consider operating even near the continuous current rating of a cell. Others would have no problem going way, way over that rating as long as the cell didn’t get hot. Neither of those is the wrong or right approach, they’re just different. They fit the way those people want to use their cells, based on their priorities, preferences, and risk-taking comfort levels.
I don’t think we’ll ever stop debating what a current rating means, not while we have so many different priorities and such a wide range of risk taking by cell users. But if we at least know what the manufacturers mean when they give a cell a certain rating that can help us to choose how hard we will use a cell.
Things to remember about current ratings:
Manufacturer’s Current Ratings
These are for li-ion round cells still in their original manufacturer’s wrap. Not just Samsung, Sony, Murata, LG, Sanyo, Panasonic, and Molicel but the large China manufacturers like BAK, EVE, CATL, Lishen, and others too.
There is usually just one rating, a true continuous current rating that gives you acceptable performance and cycle life. For the ultra-high capacity cells (>3000mAh 18650 or >4200mAh 21700) you can definitely get better performance and less voltage sag though by not going over about 50%-75% of the rating.
But there are some cells that are rated for the applications they were designed for, hard non-continuous use. Molicels are rated this way. Their current ratings cannot be used as true continuous current ratings to compare against other cells. This is not a false rating! It is the type of rating that best helps Moli’s customers judge whether the cell might be a good choice.
There’s no way for us to know this though so we are forced to check for third-party test results that can help us judge a manufacturer’s ratings. None of the round cells we use were made for individual use by end customers so this is the situation we must deal with. The datasheets and the ratings are only for the huge commercial customers for these cells.
Murata’s VTC cells (made by Sony up until 2017) also have non-continuous ratings, allowing use up to a certain temperature. But they also have a true continuous current rating you can use to compare the cells to others.
For example…
The VTC6 is rated at 15A continuous and 30A non-continuous by Murata. But if you want to compare the VTC6 to any other cell, perhaps the Samsung 30Q, then you would have to use the continuous 15A rating. You cannot say that the VTC6 has a 30A rating and blows away the 15A-rated Samsung 30Q. They are both 15A cells and perform very close to each other (30Q slightly better in my testing).
The VTC6 has huge voltage sag at 30A anyway and these non-continuous ratings are best ignored if performance is your priority.
Rewrapped Cell Current Ratings
In my opinion, “rewrapped” cells are those that have had their original factory wraps removed (or were purchased without wraps) and have been rewrapped by a company that will resell them. This is how companies like Efest, Imren, MXJO, Vapcell, and dozens of others started out.
This was originally done with cells from Samsung, Sony, Murata, LG, Sanyo, Panasonic, and Molicel but is now also being done with cells from the large China manufacturers like BAK, EVE, CATL, Lishen, and others.
The problem is that an unscrupulous company can exaggerate the manufacturer’s rating or even create their own useless “max” or “pulse” rating. The situation has gotten a lot better lately though in the US and EU, with the rewrapping companies giving their cell more accurate ratings. Some brands like Epoch, Fogstar, and others have always had accurate ratings. In Asia though the ratings on many of the rewrapped cells are ridiculously exaggerated.
There’s no way to know if the ratings on the wrap are accurate or not unless you know what cell they have rewrapped (for cells from the large manufacturers) or have seen test results.
Any “max” or “pulse” ratings can be ignored though in my opinion. I know that these are the ratings we love to see. They are ones that are listed by most vendors and they are high. But they are, at best, just the cell manufacturer’s non-continuous rating. If not then we have no idea what criteria the rewrapper used to set the rating. At worst they are merely numbers chosen during a marketing lunch meeting.
I have had multiple rewrapping companies tell me they just make up these “max” or “pulse” numbers to please the distributors who will not buy cells unless they have a big number on them. These numbers are useless marketing bullsh*t.
Some companies rewrap very good cells so don’t think that they are all to be avoided. Vapcell has gotten a couple batches of some great cells from the big manufacturers over the last couple of years and rewrap other good cells. Just stick with the continuous current rating.
As mentioned earlier, there are also great rewrapped cells from Fogstar, Epoch, and other companies.
As the cells from the big manufacturers are getting harder and harder to find (no one buys direct from the manufacturer) the rewrapped cells from the big manufacturers are becoming a smaller and smaller part of what these rewrapping companies can offer.
Many of their cells are now coming from the smaller China factories and some are pretty good. For example, the Yong De Li New Energy Corp.’s 1000mAh 18350 that at least three companies have rewrapped.
Some of us would never consider operating even near the continuous current rating of a cell. Others would have no problem going way, way over that rating as long as the cell didn’t get hot. Neither of those is the wrong or right approach, they’re just different. They fit the way those people want to use their cells, based on their priorities, preferences, and risk-taking comfort levels.
I don’t think we’ll ever stop debating what a current rating means, not while we have so many different priorities and such a wide range of risk taking by cell users. But if we at least know what the manufacturers mean when they give a cell a certain rating that can help us to choose how hard we will use a cell.
Things to remember about current ratings:
- Only use the true continuous current rating for comparing cells.
- “Max” and “pulse” ratings are useless for comparing cells. Different companies use different standards for setting these ratings or just make them up.
- The manufacturer’s non-continuous rating is limited by cell temperature and you must stop before the cell reaches this temp. Luckily it’s usually quite high, 70°C-80°C. There are a few cells that are only rated up to 60°C, easily reached in a sealed up battery pack, so check the datasheet for the cells you are using to be sure.
- Cells lose performance and their internal resistance increases over time. This can cause more heat during use and we need to take this into account as our cells age. If your cells are getting warmer but you are not using them any harder then you’ll need to lower their current rating or replace them. There’s no data available to help you know when to do this. You’ll have to use your best judgement.
- The ratings on any cell can be complete bullsh*t. This is rare for cells sold in the US and EU but is very common for cells sold in Asia. If you see a cell with higher ratings than any other similar cell it is not a “miracle” cell using some kind of amazing technology no one else has. It is just a cell with an exaggerated or misrepresented rating.
- You can use any cell at above its continuous current rating. But you lose performance, shorten its cycle life, and increase the risks. Especially as the cell ages. I recommend staying below the continuous current rating.
