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I have two Li-ion batteries in my system. (7.4 V 12000 mAh and 7.4 V 2200 mAh; also they have BMS). The larger one of the batteries can be easily removed and installed from my system, so I can charge this battery outside. But other one can't be removed so I need to charge 7.4 V 2200 mAh battery from 7.4 V 12000 mAh in a controlled way. When switch 1 is closed, switch 2 will be open, so the small battery will begin to charge. I used a boost converter to constantly charge the battery with 8.2 volts, but it got too hot, what can I use instead of the boost circuit?

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    \$\begingroup\$ Use a charger. Don't mishandle batteries like that, as mishandled batteries can get damaged and damaged batteries can be unstable and they might explode or burst into flames, leading to injuries or fires. \$\endgroup\$
    – Justme
    Commented Apr 21, 2022 at 11:38
  • \$\begingroup\$ what kind of charger ? do you have any recommend a charger circuit ? \$\endgroup\$
    – mco
    Commented Apr 21, 2022 at 12:05
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    \$\begingroup\$ Any charger that is intended for charging lithium batteries. Recommending what to buy would be off topic. \$\endgroup\$
    – Justme
    Commented Apr 21, 2022 at 12:13
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    \$\begingroup\$ None of this design is acceptable. Battery regulation must be separate to avoid long durations of > 10 min with Vbat > 3.8V (x2) in CV mode \$\endgroup\$ Commented Apr 21, 2022 at 12:13
  • \$\begingroup\$ what is your recommend ? \$\endgroup\$
    – mco
    Commented Apr 22, 2022 at 10:54

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What kind of BMS do you have? BMS's usually have overcharge and overcurrent protection, if your BMS has them you got nothing to worry about because 18650 can and will heat up a little when charged at high rate, if you don't want them to heat up that much limit the current, you should check the balance every few months if your BMS doesn't have a balancing feature.

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  • \$\begingroup\$ The batteries have BMS with over-current and over-voltage protection features. I was just worried that the boost converter was getting too hot. That's why I wanted to verify if my application was correct. Thank you for your kind reply. \$\endgroup\$
    – mco
    Commented Apr 25, 2022 at 9:46
  • \$\begingroup\$ @mco you welcome, its nothing to worry about, just make sure not to push the boost converter too far and it has some air around to cool down. \$\endgroup\$
    – Dandeson
    Commented Apr 25, 2022 at 10:07

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