makita circular saw battery gets really hot when i'm using it, is that normal or a problem?

Excessive heat is a sign of abusive conditions or a failing battery. It is a problem.

• Immediate Action: Stop using the saw and remove the battery cartridge. Place it on a non-flammable surface away from other objects.
• Do not charge a hot battery. Let it cool completely.

FIX:

1. Check your technique. Do not force the saw. Pushing too hard causes the motor and battery to overwork. The blade should cut without slowing.
2. Check the blade. A dull or dirty blade creates excessive friction, forcing the motor to draw more power and overheat the battery. Use a sharp, clean blade.
3. Verify battery compatibility. Use only specified BL1815N, BL1820, BL1830, BL1840, or BL1850 cartridges. Other batteries may create a risk of fire.

IF THAT DIDN'T WORK: The battery may be damaged. Do not use a damaged battery. Under abusive conditions, liquid may be ejected; avoid contact. If contact occurs, flush with water. If it contacts eyes, flush and seek medical help immediately.

HEADS UP: For maximum battery life, charge it before complete depletion. Do not store the tool and battery where temperatures may reach or exceed 50°C (122°F).