So you wanna buy a battery pack but you’re not sure which one to get and you are a dirty rotten cheapskate to boot. There are so many new choices on the market of batteries that completely blow away the batteries of yesteryear that before you plunk down your hardly earned dough you should have a pretty good idea of what you’re buying.
In the old days (being just a year or so ago) you were stuck with only a few realistic choices for 18650 ebike batteries. So many of the battery choices that dominated 2014 & 2015 are now pretty much old news. There are some very exciting batteries that are coming on the market that have much higher capacity, much higher discharge rates and some even now have both. This article will help you understand your options and what is the best type of battery pack to buy or build yourself.
How to calculate the discharge capacity of your batteries
When you buy a pack there are two different discharge capacities to pay attention to. One is the discharge capacity of the BMS, the other is the discharge capacity of the cells. Let’s say you buy a 52v 14S5P triangle pack made of 25R cells. You take the discharge capacity of each individual CELL (20 amps) and multiply it by the number before the P (in this case 5). That gives you a nominal discharge capacity of 100Amps (20 x 5). If this pack is hooked up to a BMS that only has a 50Amp nominal capacity then you will not be able to draw more than 50 amps continuously. Consequently, if you have a BMS which is more powerful than what the cells can put out if you run it too hard the cells will start to overheat and may trigger the temporary thermal cutoff on the BMS (if it is so equipped). Smaller packs tend to get hotter quicker than bigger packs because the load on the batteries per cell grouping is higher the fewer cells there are in a pack. Both batteries and BMS have a burst rate that they can put out for about 10 seconds or so without damaging anything. The burst rate is usually quite a bit more than the continuous rate.
Good capacity or good discharge rates but not both
The rule of thumb for the olden days was you had to pick a battery that had good capacity (the amount of energy it can store) or a great discharge rate (the amount of energy it can provide continuously without overheating) but you really couldn’t have both. The only two cells that are still relevant from the olden days are the 25R and the 29E cells. The 25R is one of the most insane 18650 cells ever made with the ability to put out 20 amps sustained for extended periods without overheating. This cell has been tested with a maximum burst rate of over 100Amps. The 25R still stands alone as a cell that has a discharge rate that nothing else can touch. The downside of course, is the capacity which is 2500Mah tested with a 2Amp continuous drain. All manufacturer rate their batteries with a 2Amp drain, so you better believe when you hook it up to your ebike and pull 20 Amps continuously out of it for an hour you’re NOT going to get that full rated capacity out of the battery. If you pull more power than 2Amps then the capacity will drop, some cells this happens more than other. I can still recommend the 25R cell for packs bought today because nothing comes close to it for the price\performance and it still is an excellent high discharge rate cell for ebike packs.
The 29E is an older high capacity cell that still has a decent discharge rate and it used to be a favorite for large high capacity packs. Samsung rates the 29E cells at 2.75A continuous and 8.25A burst, but if you want the cells to last for any period of time you should not run them at much more than the 2.75A for any real length of time. That means on a 5P pack that the continuous discharge is going to be around 13.75 Amps which is painfully low for a real ebike. I do not recommend this cell, but I’m just using it to show how far we’ve come in the last year.
Brand new cells I’m really, really excited about
There are over a dozen cells that have hit the market this year but there are 4 cells that I have experience with that I’m really excited about that I’m going to write about. Each of these cells has benefits and drawbacks, but each of them fills a price\performance niche that has not been filled by the older style cells.
Panasonic NCRb, a very high capacity, relatively inexpensive, lower discharge cell
The NCRb is a pretty amazing cell in that it puts out 3400Mah with a 6.8Amp peak output. This cell gets pretty hot when you draw more than 6 Amps continuously out of it. I got a 4P shark pack from Lunacycle.com which I reviewed here as ‘the best pack I’ve ever owned’. The pack has insane range and works well with the 25Amp BBS02, although it gets too hot when paired with a 30Amp BBSHD. When you want to use a smaller pack with a high power draw application you are better off going with the PF or GA cells which cost a little more. The NCRb is being used in some Teslas and if you don’t abuse it, this battery should give you many, many years of power.
Panasonic PF, a decent capacity, inexpensive, high discharge cell
The Panasonic PF is somewhere between the NCRb and the GA cell both in terms of cost, capacity and discharge rates. With a 2900Mah capacity and a 10Amp continuous discharge the PF cell sets a new bar for high power cells. The best part is that the PF cells are not that expensive. With a 4P frame pack you can get 40Amps of continuous power with the pack barely getting warm, with a 5P pack you can get 50Amps continuous which is enough to satisfy the appetite of almost every ebike builder out there.
The Samsung 30q, Similar to the PF although with a much higher discharge rate and more expensive
The 30Q has a 3000Mah capacity and a whopping 15Amp continuous discharge rate. This cell has been tested by several reputable vape sites and it actually does very well up to about 20Amps. Above 20Amps discharge per cell you’re better off going with a 25R. I have a 30q pack (reviewed here) that I really love for higher power applications, at 40 Amps of continuous draw with a 7P pack these cells don’t even get warm (although that same power draw really heat up my large 20Ah 26F pack). This 7P pack theoretically would perform very well at 105 Amps of continuous discharge which is way more than the 50 Amp continuous BMS is going to allow. The 30Q cells are amazing both in their capacity and their discharge rate, but performance like that comes at a cost, a higher price than the above-mentioned cells.
The Panasonic-Sanyo GA cell, Finally a high capacity, high discharge cell for the masses
I’m saving the best for last and the joint venture between Panasonic and Sanyo has created a real monster : The NCR18650GA cell. This cell does not even get warm at it’s rated 10Amp discharge rate and stores an insane 3500Mah per cell. There is some speculation that this could actually be an 11 or 12 Amp continuous discharge cell that is conservatively underrated. Eric from Lunacycle went crazy with this cell and bought way more than he should have so he is selling these cells wholesale right now at a mere $6 a cell (basically at cost) in quantities of 50 right here. I bought 2 boxes which is enough cells to put together a 7P pack which will have 24.5Ah or power and will not even get warm pulling 70Amps and will weigh in at a svelte 12lbs. If you’re too lazy to build this pack yourself from scratch you can buy a triangle pack here for $729, but do it fast because they will certainly sell out. To give you some idea of how much battery technology has advanced my old 25Ah 52v LifePo4 Prismatic cell battery that was top of the line last year weighs in at 25lbs and can only put out a mere 30 Amps continuous. I predict that within a year the GA cell will become the new 25R cell completely dominating the high power ebike battery scene. For the full specs on the Panasonic GA cell click nhere.
There are a LOT of counterfeit 18650 cells on ebay and alibaba\aliexpress (almost all of them actually). If you’re trying to buy a few individual cells then I strongly recommend buying from a reputable vaping or flashlight company (I use wakandvape.com because it’s owned by Eric and I’d trust him with your life, but probably not mine). There are also a few places to buy cells at wholesale, check the bare cells listing under Lunacycle if you can afford to get them 50 at a time. If you buy a 100 then you can build a 14S 7P pack with only 2 cells left over, you can find a variety of 14S BMSes right here. My advice is to buy from a reputable cell dealer, if you’re not sure then post a question on endless-sphere before you pull the trigger and give anyone your credit card number.
Other new cells I didn’t mention because I’ve never used them
There are a lot of 18650 cells on the market that I didn’t mention in this article. I only wanted to talk about the cells that I had personal experiences with. For a more in-depth article with lots of information on new cells check out this article on our evil twin sister blog electricbike.com written by the all-knowing-ebike god spinning magnets. The article is about 8 months old but the information is still quite relevant today.
So what ebike cell should you buy? I recommend figuring out first if you’re going to go with a 48v (13S) or 52v (14S) pack. I almost always recommend going with a 52v pack unless your controller can’t take the power (most 48v controllers can). Once you figure that out you need to figure out how much continuous power you need to provide and purchase the battery pack according to your power requirement. Lets say you have a BBSHD and want to be able to run at 30Amps all day long. If you go with a 4P pack like a shark pack you will want to avoid the NCRb cells because they will get to hot at those power levels. The PF and GA cells are both good choices but a 4P 30Q or 25R pack is a total overkill and you should save your money. If you had a 25 Amp BBS02 and wanted to go with a 4P pack or larger then I would say that only the NCRb packs make any sense as if you get anything else you are paying more than you have to for capacity that you’re not going to use. The 25R cells are a good choice if you want a tiny pack with a short range for a higher power ebike. A tiny 28 cell 2P 25R pack will give you only 5Ah of range but will give you 40Amps of continuous power (200Amps burst). If you are in doubt about what is the best pack to use for your application then you should ask the ebike battery dealer and they can always point you in the right direction.
In short, with the exception of the 25R cell I would avoid the cells of yesterday and focus on the packs of tomorrow. Buy an ebike battery pack that will not only provide for your current continuous power needs, but will also be able to provide power for your future, slightly more powerful builds. If on the other hand, you know you’re going to be happy for several years with the ebike you currently have then don’t buy a cell that costs more and has a much greater capacity than what you need.
No matter what you chose in 2 or 3 years your pack is going to be obsolete anyway, so might just as well suck it up. You gotta pay to play.