Li-Ion Batteries for flying RC models

I fly my RC Airplanes and quadcopters on LiPo batteries like most other people. But LiPo batteries have several disadvantages. The biggest problem is that their life is pretty short. They usually don’t last more than 100 cycles. Therefore I wanted to explore the possibility of using 18650 cells to power my RC models instead. I while ago I got myself a cheap battery spot welder from China and a couple of genuine LG HG2 cells.

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I choose LG HG2 cells since they have one of the highest discharge ratings on the market, 20A continuous and 30A burst, in combination with a high capacity of 3000mAh. There may be other cells that can handle more current, but they have far less capacity.

This was my first time ever trying to spot weld batteries, so I tested on an old NiMh battery pack I had lying around. I pried off the old connections and remade them myself. After feeling comfortable I started working on the real cells.

I glued the cells together using some hot glue and cut some pieces of the widest thickest nickel strips that were included with the spot welding machine. After all the welding was done, I soldered on a charge/discharge wire with an XT-60 connector and a balance wire to the pack, then wrapped it in some heat shrink.

The final 4-cell battery weighs about 200 grams and has a capacity of 3000mAh. This can be compared to a 200 gram 3-cell LiPo battery with a capacity of 2200mAh which I usually fly my model airplanes on. The weight is the same, but the voltage is higher and the capacity is significantly larger. The total energy stored in the Li-ion battery is about twice as much as the LiPo battery with the same weight. Theoretically, this should double the flight time of any model airplane.

The Li-ion cells can be charged up to 4.2V, which is the same as LiPo cells, meaning I can safely charge this battery using the LiPo setting on my charger. My charger also has a Li-ion mode with a slightly lower end voltage, which is probably better to use. The cells can be discharged down to 2.5V per cell without being damaged, which is far less than the 3V of LiPo cells. This means less chase of damaging the battery when draining it to mush.

So far I have built two of those battery packs. I have only flown with them a couple of times, but so far they are performing well. Looking forward to testing those more during this summer…

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