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I'm building an autonomous boat (which needs to get me a bottle of fine whisky from Scotland) for which I want to build a battery pack. The boat is currently powered by a cheap Li-ion battery pack, but I want to build my own battery pack so that I can better determine the shape of it to fit it in the boat

After reading around I decided I want to build a LiFePo4 battery pack, mainly because it's more chemically stable and heavier (I actually need the weight). The battery format 18650 seems to be the most standard, so it seems logical to go for that. As far as I understand I need a spot welder to connect the batteries together. A spot welder seems really expensive though and I don't really need it for anything else.

While searching I also found these batteries with tabs on the poles (see image below). My question is whether these can be used to build a battery pack without the need for a spot welder? Maybe I can simply connect them by soldering wires on to them?

The battery will only be charged very slowly by day, and be discharged relatively slowly by night (maybe 12V*1.4Amps=16.8 Watts or so discharge), so I don't think the wiring will become very hot.

Are there any downsides to not using a spotwelder? Is there any serious drop in performance? Or any other dangers I'm unaware of? All tips are welcome!

enter image description here

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    \$\begingroup\$ Sure there are downsides to soldering, but it is not like you have a choice, unless you want to spend $$$ to get a spot welder. If soldering directly to the cell, use flux and a BIG (>4mm, even 6mm or 8mm) short, fat iron tip with lots of contact area and be fast to get in and get out. Tabs are safer and easier but less compact. \$\endgroup\$
    – DKNguyen
    Mar 10 '20 at 16:12
  • \$\begingroup\$ @DKNguyen - Ok, so are you saying that if I use the tabs, the only downside is that they are less compact? Because I could live with that. \$\endgroup\$
    – kramer65
    Mar 10 '20 at 16:59
  • \$\begingroup\$ That's probably the biggest one by far. \$\endgroup\$
    – DKNguyen
    Mar 10 '20 at 21:17
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Sure there are downsides to soldering, but it is not like you have a choice, unless you want to spend $$$ to get a spot welder. If soldering directly to the cell, use flux and a BIG (>4mm, even 6mm or 8mm) short, fat iron tip with lots of contact area and be fast to get in and get out. Tabs are safer and easier but less compact.

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