Why would it just lose power as if disconnected from the battery but isn't

Hi - I am Dave, contributing to RepairPal and providing expert advice since 2010. If the battery in the key were bad or low in charge it should be replaced - but will not cause this concern. Stalling on deceleration is an engine performance concern - testing must be performed to see what is happening with fuel, spark and air. Get some help from a shop near you: https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.