Anything that has radios in it, such as devices with bluetooth, are going to see peak currents in the amps.
I've designed and worked on a number of devices that are very similar to these wrist bands. The typical modes are uA draw for long sleep periods, 10s of mA while collecting data/doing whatever for milliseconds, and 500mA to 2 or 3A for a few hundred ms every once in a while to transmit data.
So low ESR, high power capable batteries are very desirable for this sort of device. Especially when you consider that 2A draw is likely around 20C out of a wearable battery!
Please point me to one of devices you worked on that is wearable and draws 3A when transmitting. I would also love to see a BLE device with power consumption in the amps, especially considering TX power limits in the standard. Its normal for Class 3 BLE radio to consume same current when transmitting as when receiving (in <20mA range).
I've designed and worked on a number of devices that are very similar to these wrist bands. The typical modes are uA draw for long sleep periods, 10s of mA while collecting data/doing whatever for milliseconds, and 500mA to 2 or 3A for a few hundred ms every once in a while to transmit data.
So low ESR, high power capable batteries are very desirable for this sort of device. Especially when you consider that 2A draw is likely around 20C out of a wearable battery!