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I want to build a battery for an electric bicycle using 18650 batteries. But I'm not into spot welding so much. Would it be possible to build a large case for the 18650 batteries with these types of black plastic cases serial connected together and then just put the batteries in place when I want to use them instead?

batteries

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  • $\begingroup$ Sure -- just ask Tesla Corp. $\endgroup$ – Carl Witthoft Jan 2 at 16:36
  • $\begingroup$ I know of one electric boat that used lithium D cells in pvc pipes (with full cell by cell monitoring, cell by cell charging, and forced air cooling). The guy used tiny magnets between the cells and a big spring at one end. He ended up with a few hundred cells in the system when he was finished. He was a retired electrical/electronics engineer, so that helped a bit. And he spent a couple years prototyping and testing before it went on the boat. This is not a trivial task to get right. check out the BMS systems for similar arrangements such as those for Torqueedo. Figure 1$ per Wh. $\endgroup$ – Phil Sweet Jan 2 at 22:12
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From a strictly electronic point of view, one can construct a larger battery using the cases you've posted. In your example, an electric assist bicycle, you will have relatively high current draw requirements. The wiring and spring loaded contacts will fare poorly under such high currents.

It's possible that the wires will melt the insulation due to the heat generated, or the spring contacts will get hot enough to cause the case around them to melt. Once the insulation is melted, short circuits can occur.

It's common for batteries for e-bikes to be rated to 40 amperes current draw and those wires and contacts will not tolerate the level.

With soldering of this type of battery, the heat from the tool will likely damage the battery and might cause explosion. Multiple batteries composed of this type of cell use spot welders specifically made for this purpose. You can find a DIY resource by searching "DIY battery spot welder" for options to complete your project.

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Any type of welding is not a good idea. But more to the point - if you don't include load-balancing electronics both for charging and discharging, you will be VerySorry(TM) .
To start out, you should read up on topics such as "Charge in parallel, discharge in series" depending on the anticipated charging voltage and output/drive voltage intended. each cell can only put out its own rated current (without voltage sag), and can only charge up to certain voltages and current rates; those current rates vary dramatically with the charge level of the cell.

There's a reason that Tesla Corp's vehicles have gigantic amounts of hardware and software control of the battery packs.

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  • $\begingroup$ Some types of welding are not good methods, but spot welding of batteries is common. sunstonewelders.com/applications/battery-tab-spot-welders offers products to enable others to create battery packs the correct way. There are many other related resources, too many to list in a comment. $\endgroup$ – fred_dot_u Jan 3 at 1:07

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