I bet:
- the temperature has just dropped and the weather your way has gone cooler.
Check:
- battery fluid level
- battery acidity (garage test)
- fan belt tension
- that the battery terminals are both shiny metal clean (use a wire brush) and greased with Vaseline
If it's still giving problems, take the battery out, wire a headlamp bulb across the terminals (with heavy wire) and burn the battery flat overnight. Check the fluid levels, top up with distilled water if necc. Recharge the battery on a low-rate charge over 1-2 days. Re-install and run the car for a while to charge it up further before serious use.
If it's still giving problems, take it in to the garage and get them to do a charging system check (battery and alternator together).
If all is OK and it still gives trouble, check your wiring to the sled.
If it's still giving problems, give up.