How long do chest strap batteries and straps last?

It varies by model. Coin-cell straps like the Polar H10 are reported to run roughly six months to a year of regular use, with the fabric strap itself wearing out after around a year or 800 uses according to Polar community posts. Rechargeable models such as the Wahoo TRACKR and Garmin HRM 600 avoid coin-cell swaps but add charging to your routine.