The sound tells you first. The engine turns over slowly, or the car clicks once and goes quiet, or the dashboard light dims when he turns the key. Those are the usual signs that the battery has lost the strength to start the car. The question is whether to swap it yourself in the driveway or hand the job to someone who does it every day.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Check the cheap things first
Look at the two posts on top of the battery. White or blue crust on the clamps means the connection cannot carry the current even if the battery is fine. Loosen the clamp, clean it with a wire brush or a rag, and tighten it back. Then wiggle each cable by hand. If it moves, it is loose, and that alone can cause the clicking.
Next, check the battery itself. A cracked case, a bulge, or liquid on the top means stop and call someone. Many parts stores will test a battery for you, which tells you whether the problem is the battery or something else, like the starter or the charging system. Ask them to print the result, not just tell you the answer.
Decide: yourself or the shop
Swap it yourself if the battery sits under the hood in an open spot, is held by a single bracket, and the car does not need a computer reset afterward. You need a wrench, safety glasses, and the strength to lift the battery without straining.
Call the shop if the battery sits under a seat, under a panel, or in the trunk. Call the shop if the car needs its windows or radio reset after the power comes off, or if the battery warranty depends on who installs it. Ask the shop what they charge to install a battery you bring, and what they charge if they supply it. Ask whether the warranty is honored at their location. Those questions settle most of the choice.
Doing the swap safely
Turn the car off, take the key out, and keep sparks and cigarettes well away. Disconnect the negative cable first, the one marked with a minus sign, then the positive. Set the new battery in the same position, connect the positive first, and the negative last. Tighten the bracket so the battery cannot move. If you notice a sulfur smell or any leaking, stop and call someone. Keep the old battery upright and take it back to the store that sold the new one, since many stores accept old batteries for recycling.
What to do tonight
Pop the hood with him standing next to you, so it stays his car. Look at the clamps, check the battery for cracks or swelling, and write down the size code printed on the label. Don't try to jump it from a neighbor's car if the case looks damaged. Find the warranty card and keep it in the glove box where he will look for it.
When to call a shop right away
Call if the battery is cracked, leaking, swelling, or smells like rotten eggs. Call if the clicking continues after the clamps are clean and tight, because the starter or charging system may be the problem. Call if the car is newer and has a battery monitor, since it may need a reset that most people should not guess at. There is no shame in handing this one over.
A good-week note
A good week is one where the car starts on the first try, the battery has been tested, the warranty card is in the glove box, and he knows which option he picked and why.