Highly unlikely both carts would fail, check the rest of your chain and do the above and check with a multi-meter the continuity of the coils in the carts.
that said the coil wire is very small think smaller then a hair, so if not stored in a clean dry environment they could degrade over time.
that said the coil wire is very small think smaller then a hair, so if not stored in a clean dry environment they could degrade over time.