If you have to go and Li-Ion chem and if range is no issue with a 6P setup (I'd say 25 miles), Id go with Sony VTC4... Thes cell will run coll because they have low internar resistance (21 mOhm DC IR), thus very good cycle life.
If really you don't care for range for a 6P setup (think 12-15 miles) and you want inclredible cycle life and 10 year + lifespan, go with A123 LiFePO4 nanophosphate cells ( mAh, yellow wrapped cells). Very very low internal resistance. Very good discharge rate. Will run super cool in your setup. But range sucks... On the plus side, charge rate can be quicker on LiFePo4.
But consider this 250W is such a soft setup, even running cells rated for max 10A discharge rate in a 4P configuration should last a good 3 years (just don't store at 4.20V)… So if it's range you are after Samsung 30Q ( mAh, 15A) or MJ1 would be a well balanced solution. You could also go Panasonic GA mAh 8A cell and they should still last 4-5 years.
If you can exit the format for something bigger format,
Then consider A123 MA1 LiFePO4 nanophosphate mAh cells. Best cycle life, but bulky and heavy for a not so great range (think 30 miles for a 6P setup).
I would personally go with the Samsung 40T cells. 30A rating means the have pretty low internal reistance (meaning they run cool and thus good cycle life) and at the same time have mAh capacity and don't tale so much space or weigth too much. Just, they are a bit pricy cells.
Think about it a 6P setup of samsung 40T cells at 36V, thats 864Wh of capacity and a max discharge rate of 180A, that your bike will baby up at 7A continuous and 15A burst.
With a 250W eBike, you really have a lot of options as most ebike battery will survive very long du to very low current stress. For range you can expec 10Wh per kilometer so around 80-85 km (50 miles) good enough ?
But to be frank, alhough the worst posaible option for cycle life, you could even get away with 6P of laptop cells for such a low power 250W setup (1.2A/cell continuous ; 2.5A/cell burst). Not that i would recommend that last option.
So choice is hard to make because there a just som many options. What would help is to define exactly what kind of range you need. Would you want smaller than 6P ?
Pretty simple choice IMO. Pick the lowest internal resistance cell you can afford.
Even though your setup will not challenge a good cell like the Samsung 30Q, any cell will last longer if you don't get it hot. Cooler the better, not meaning cold weather, but meaning not having a pack that gets almost too hot to hold in your hand each cycle. Cheap no name cells will do that, under fairly low amps too. But that cheap pack, it will still go 2 years, and 500 cycles.
Any of the better cells you mention should go double that, on your typical amps draw. Especially if you balance them at 4.1v. Most bms goes to 4.2v, so you might end up doing a weekly charge to 4.2 just to get them balanced. Just ride it down to lower voltage immediately, and the higher charge will do little harm.
If you don't go , don't fail to consider RC lipo. Touchy cells to be sure, but cheap, and you run 20 ah of the 30-60 c stuff at less than 1c, and the pack will be stone cold the whole ride. And you will get three years from it for sure. I like to buy 10 ah of it each year, and then run it in parallel with other packs that are one or two years old. Small and affordable buy every year, but always have up to 30 ah of it around.
Thank you so much for your insight, everyone
Matador said:
[...]
For range you can expec 10Wh per kilometer so around 80-85 km (50 miles) good enough ?
[...]
So choice is hard to make because there a just som many options. What would help is to define exactly what kind of range you need. Would you want smaller than 6P ?
[...]
I ride 100km on long days, but I live right in the city center, so I can swap battery packs at home once or twice a day. So I thought the best option was to get 2 packs around 600Wh-700Wh each and cycle them between 4.1V and 3.3V.
I would like to go with Reention or Hailong battery packs, because I find the form factor very convenient. (If there are better options out there, I'm always grateful for brainstorm inspiration!) They come with cell holders, so using different battery sizes would mean a lot more work when building packs.
the best thing is to find a space on your bike that can store as many cells and humanly possible.
1 battery made of 100 cells lives 4 times as long as 2 batteries of 50 cells each.
and it saves you recharging swapping batteries because that shit needs to happen at the worst time.
because you already have a delivery bike you are already hauling weight. having 1 big battery instead of 2 smaller ones that you need to swap gets old really fast and after a while you dont notice the extra weight and you can crank up the power more without damaging/wearing the pack much.
having a bigger pack also helps a lot during cold or really hot weather as the temperature is more even and you will get more consistent performance from it and dont have to worry as much about heat.
vulcanears said:
The controller is 7A continuous, 15A peak. (Which is the legal limit in the EU)
As others have said, managing charge/discharge maximums/minimums, and over-building pack is the best way to achieving long life from your battery pack. Also, choose a tried-and-true cell (Sanyo 29E is a good one)...it may not be the best power density or maximum amp ratings...but in the long run it has a proven track-record.
FYI if you motor is rated at 250W, the only way it would ever draw 15 amps is maybe if it was stalled (not turning at all).
The controller's maximum amp rating is only a rating which the controller can handle....it has little (maybe lower resistance, so less wasted power generated as heat) bearing on how much current is actually delivered to the drive motor. That is a function of maximum voltage of battery and resistance and KV of motor. If motor is rated for 250W at a specific RPM, then the motor will only draw about 6amps under load at the maximum wattage rating of motor.
PS: My controller is rated for 38amps....500W motor never draws more than 20, and that is on the hills.