Fitbit Charge 4Fitbit Versa 2
Tech specs 
SizeDevice Dimensions: 42.7mm x 28.8mm x 12.5mm
One size (small and large bands included)
Screen size 40 x 40mm
Small: Fits wrist 140 mm - 180 mm in circumference
Large: Fits wrist 180 mm - 220 mm in circumference
MaterialBuilt of more lightweight material including an aerospace grade aluminum case and Corning Gorilla Glass 3 display. The housing and buckle are made of anodized aluminum.The classic band is made of a flexible, durable material similar to that used in many sports watches, and includes an aluminium watch case and buckle. The woven band is made from a comfortable polyester and includes an aluminium watch case and buckle.
Battery lifeup to 7 days, or up to 5 hours with GPS. 5+ days. Charge time (0-100%): 2 hours.
Water-resistance5 ATMup to 50 metres (swim-proof) - 5 ATM
Weight30 grams40 grams
Sensor3-axis accelerometer, Optical heart rate monitor, Pulse Ox, GPS, Vibration motor, NFC chip for Fitbit Pay, Altimeter, Bluetooth LE (BLE)3-axis accelerometer, Optical heart rate monitor, Altimeter, Ambient light sensor, Vibration motor, Wi-Fi antenna (802.11 b/g/n), Relative SpO2 sensor, temperature sensor, NFC, Built-in microphone
DisplayOLED full touchscreen, TFTColour AMOLED touchscreen, 300 x 300 pixel resolution
Screen size35.8mm x 22.7mm1.4 inches
ColorsMultipleComes in a number of colours. Also there's a regular and special edition (which comes with an additional woven band and 90 day trial to Fitbit Premium).
OtherCharge 4 stores your stats and data for 7 days in between the times you sync your tracker.- Saves 7 days of detailed motion data, minute by minute
- Saves daily totals for the last 30 days
- Stores heart rate data at 1-second intervals during exercise tracking and at 5-second intervals all other times
Activity tracking 
Calories burnedYesYes
SleepYesYes (light, deep & REM)
Heart rate24/7 + HRV (premium subscription)Yes + HRV (premium subscription)
Stress & recovery
Pulse OxYesYes
Respiration rateYes (premium subscription)Yes (premium subscription)
UV exposure
Skin temperatureYes (premium subscription)Yes (premium subscription)
Galvanic skin response
Hydration level
Calorie intake
Running features
Swimming features
Other Guided breathing, Female Health Tracking, Spotify control- Guided breathing sessions
- Female health tracking
Non-fitness functions 
Smartphone notificationsYesCall, text and calendar notifications
On-board music storageYes, 2.5GB (300 songs) + access Pandora, Spotify, Deezer
Connected payYesYes
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