If you're not getting the modular batteries (and are buying individual 26650's) Expect to spend a good chunk of money on a welder or having someone weld them together for you.
The quality varies a TON between individual 26650 cells.
I've built several K2 packs for two different electric motorcycle companies, both with K2 26650 cells, both with less than expected results. They vary way too much between cells. They're "OK" cells, but if you want performance, you might look at other batteries. Maybe they've gotten a little better, but I don't know if I'd want to spend a bunch of money just to have to test them all.
With a relatively untested product like those assembled packs I'd definitely at least test a couple of them; before spending the money on enough of their packs to power an EV. Unless they were willing to give you a good warranty guaranteeing a certain level of performance of the packs. Especially with some of the lackluster reviews that are out there about the individual cells.
If it takes that much effort just to buy something from them, imagine what kind of response you'll get if you have problems...
thats why I said "if you're not getting modular batteries".... which is what you were obviously considering.Thats makes no sense to me, K2 Energy builds their modular packs with 26650 battery cells. The packs are "welded" by the company. You can buy the packs or the cells. My only hesitation is the quality of building their packs, they 'welds" must be perfect. I am waiting for technical response from the company.
I have a 3s1p pack of K2 26650 "energy" cells right here rated for 3.2Ah (10.24Wh @ 3.2V) that deliver a peak current of 118A for 0.5 second. So, 37C. Probably not the best choice for drag racing, but pretty good for a power tool (which is what this little pack is for).thats why I said "if you're not getting modular batteries".... which is what you were obviously considering.
The batteries just don't perform that well. Get some headways or lifebatt.
I have a 3s1p pack of K2 26650 "energy" cells right here rated for 3.2Ah (10.24Wh @ 3.2V) that deliver a peak current of 118A for 0.5 second. So, 37C. Probably not the best choice for drag racing, but pretty good for a power tool (which is what this little pack is for).
Rebirth Auto just received a bunch of both 8Ah "power" and 10Ah "energy" Headway cells but I haven't messed around with them at all yet. Might get a chance to do some peak current testing on them later today.
Lifebatt cells are still a total unknown to me. - has anyone here actually bought any to test? Also, the fact that someone who is clearly connected to them - the username "Lifebatt" sorta gives it away, I guess - only shows up here every so often to trash-talk the competition and post pictures of Taiwanese chicks waltzing around generic industrial equipment in surgical gowns isn't terribly promising to me, but perhaps I'm being overly cynical?
I'm using the old grey 10Ah cells in my motorbike (see signature link). I've only pushed them to around 7C so far, but they seem to perform very well. I'll get some more precise figures when the snow has gone. Jozzer on here has plenty of experience with pushing these cells on his motorbikes. As mentioned, the UK and US arms of Lifebatt seem to be selling different cells now.Lifebatt cells are still a total unknown to me. - has anyone here actually bought any to test?
Malc has the older LifeBatt cell manufactured by PSI, these were a great cell for an everyday ride. I believe they are still available around and about..
Indeed, the US lifebatt rep has different cells. I have tested a pair sent by Michelle/Don with less than conclusive results. Seem to be good for 10C peaks, fair for a road motorcycle but not good for drag racing IMO.
The same is true of Headway, both manufacturers use the same criteria to determine peak power, which seems to be that the voltage stays above 2.1v. Losing 30% of the power under heavy load is ok for a quick getaway at the trafficlights, but is not acceptable for a race vehicle IMHO, it would meam carrying 30% extra cells to maintain voltage to maintain current at top speeds. This lost power of course will turn up as heat in the pack, which will affect cycle life profoundly).
Also to consider is that LifePo4 weighs some 30% more than high rate LiPo.
For a racing vehicle of any kind there are really 2 possibility's, the very best of the LifePo4 (this means A123 only as far as I can tell), or decent high rate Lipo's. Kokams are one choice here, but far cheaper and perhaps more power dense are cells from the RC world. The Lipo packs in my TTX02 race bike sag 3% under a 9C load at any point in the charge cycle (even 70% discharged).
The down side of these cells is lifecycles, paerhaps 200-250 before 20% capacity is lost, compared to 1000+ of LifePo4 (3000+ in the case of A123)
For the record, I have tested and used all cells mentioned above with the exception of the Kokams both in the lab and with vehicles on the road and racetrack (though not dragstrip).