Read the rules carefully. Forbidden are lithium METAL batteries (non-rechargeable) with over two grams Li. The rules you are concerned with are those for Li ION batteries (rechargeable).
You need to check the watt-hours of your battery. Often a battery will express milliampere-hours - I believe if you multiply this by the voltage and divide by 1000 you will have watt hours.
The reason for the new rules is that Li batteries are a very concentrated source of energy. Shorting of the terminals turns them into at best an incendiary device and at worst a bomb. That is why different rules apply for batteries in a device - that provides protection against shorting.