What are the signs and symptoms that might make you think your vehicle needs a tune-up? A misfiring engine (when spark plugs ignite at the wrong time) could be caused by worn or fouled spark plugs. Bad spark plugs can also cause low fuel economy, hard starting and sluggish acceleration. Most plugs, though, should last 100,000 miles or more, and engine computers do a remarkable job of compensating for worn plugs, so that might not be the main or only culprit.
If the battery terminals are clean and tight, then the next item to check is drive belt tension. If the belt which drives the alternator is too loose, then the alternator will not produce enough electrical current to keep up with demand. Many modern vehicles utilize a single belt which drives the alternator and other accessories. This system usually also has an automatic belt tensioner which always maintains correct tension and is not adjustable. If your vehicle uses a wide, multigrooved or so-called "Serpentine" belt to drive the alternator, then it likely also has an automatic tensioning device.
"Heat kills car batteries," according to John Banta, a Consumer Reports project leader and part of the team that tests batteries for the magazine. "Many times in cold climates, your battery fails to start your car on a below-freezing day. The reason this happens is that the heat of the past summers has weakened your battery. When you use it in the cold, the starter requires more electrical current to turn over the cold engine with its thickened oil." Leaving your car parked or stored for long periods of time can also lead to a dead battery that you will need to recharge before heading out for a drive.
In case you don't know who take your car to for auto electrical repairs, you can ask for references from fellow motorists; ideally friends and relatives who are unlikely to mislead you in this (potentially sensitive) matter. As long as they have faced such situations before, they are likely to guide you on which service providers to visit; or at least which service providers to avoid.