I'm in the process of building an electric motorbike and was taken aback by the cost of the batteries. To save some cash, I'm exploring the option of using used 18650 cells, but I can't find much information online to help me decide if they're safe to use. My setup will be running at 30A and 48V, and I'm planning on making two battery packs, either with 7s5p or possibly 7s6 (since I don't have space for a single 14s5/6p configuration).
For context, used cells cost about 5.83 reals each for 3C 2000-2100mAh, while a new EVE 26V 7.5A 2450mAh cell goes for around 14 reals. The used cells might operate at 5A per cell, whereas the new ones could handle up to 7A.
To give you a clearer view of the costs involved: I'm considering buying 84 used cells for a total of 490 reals or going for 63 new EVE cells for about 849 reals. I'm interested to hear what you think about using the used cells!
3 Answers
It really comes down to the quality of the used cells. You should definitely test them for both capacity and internal resistance before making a purchase. I picked up some Samsung and Sony packs for my electric moped, and they still function perfectly after three years because they were over 90% of new capacity. Always double-check what you're getting!
I bought some cells from a guy who only checked capacity and voltage. They came from laptops, and he had plenty of sales under his belt. Should I trust that sort of vendor?
The safety of using used batteries really hinges on how well they're balanced in their pack. Imbalances can lead to greater wear on weaker cells, making them less reliable. So if you're going with used cells, I’d suggest sticking with setups where imbalances won't be a huge issue, like single-cell applications or designs that can balance the wear effectively. Just remember, balance is key!
I'd be careful with those prices! A couple of years back, I got some new 21700 cells for my ebike build and they were only around 4 USD each. Just make sure you're sourcing from reputable vendors rather than settling for the cheapest options—quality matters!
I’d be cautious; try to find someone who does a more thorough testing, or at least get a warranty of some sort if you're going used.