You should never charge your e-bike battery unattended! But with the right safety precautions, you can charge it indoors.
Place the battery on a fireproof surface and away from flammable objects for charging. The VLITEX e-bike battery bag or the VLITEX fire protection blanket, for example, offer good heat resistance. They are also available in small formats that are suitable for rechargeable batteries or e-bikes.
Silicone-coated glass fibre fabric withstands temperatures of up to 1,000 °C.
If you charge the battery in the VLITEX e-bike battery bag, make sure that the temperature does not get too high. The first thing you notice when your battery is defective is that it becomes unusually hot.