While few drivers know how to test batteries or own the "multimeter" needed to do so, mechanics and auto-parts stores will often check for free. AAA and other auto clubs also generally offer complimentary battery testing, just so they don't have to provide roadside assistance later.
Once the battery has been checked out, the next step is removing any corrosion -- the white powder that builds up on the terminals, reducing contact between the battery and the starter motor. Having a professional clear corrosion is a good idea for novices, as batteries contain dangerous acid. Many mechanics will clean batteries for a small fee or as part of a larger job.Do-it-yourselfers
will need rubber gloves, eye protection, baking soda, water, and an old toothbrush, and should remove metal jewelry before starting. Mix some baking soda and water and pour an ounce or so onto any visible corrosion. Don't worry if the powder starts bubbling -- that's normal. After a minute or two, use the toothbrush to wipe the corrosion away. (Don't blow it away, as it could get in your eyes.) To be really thorough, unhook the battery cables and remove corrosion there, too. But beware: Disconnecting a battery runs the risk of setting off a vehicle alarm or losing car-radio presets.