My 85 chevy truck won't start when it is cold, unless I put it on a charger.

You might have your starter checked.

Have your alternator checked. May be going bad and producing less power than is needed to recharge the battery fully causing a slow drain of power in the battery till starting the vechicle cannot be accomplished.

YOU MAY HAVE A BATTERY DRAIN CAUSING THE BATTERY TO GO DEAD AFTER A COUPLE OF DAYS. TRY DISC. YOUR BATTERY WHEN TRK IS SITTING FOR THOSE 2 DAYS AND SEE IF IT STARTS.