Semi truck won't start: dead batteries on a big rig, and what to have ready

Why big rigs go dead

Most heavy trucks run a 12-volt system with several batteries wired together, though a few use 24 volts, so say which if you know. A heavy diesel needs a lot of current to turn over. Trucks also run loads while parked: sleeper heating or cooling, a refrigerator, an inverter, lights. Add a weak alternator, loose or corroded cable ends, or batteries that have aged, and the truck won't turn over.

Cold makes both halves of the problem worse, since the engine is harder to turn and the batteries are weaker. The first cold morning of the year is when a bank of aging batteries tends to give out.

What to check first

Before you call, a few minutes with the truck can save a trip:

• The battery disconnect switch, if the truck has one. It is easy to leave it off after maintenance.
• The cable ends at the batteries, which may be loose or corroded.
• The dash lights. Dim means weak batteries. Dark means a disconnect or batteries that are fully dead.
• Any battery that looks damaged: swollen, cracked or leaking, especially after a cold night.

Why a small jump pack isn't enough

A starter on a heavy diesel pulls far more current than the one on a sedan. A small jump pack that works on a car may not turn a big diesel over. That is why a semi gets a heavy-duty jump start, and why the truck should be requested as a semi, not as a car.

For the same reason, a passenger car is a poor donor for a big diesel. It usually can't supply enough current, and it strains its own electrical system trying.

What to have ready when you call

Choose Semi truck as the vehicle type when you request help, and have these ready:

• The unit number.
• Exactly where the truck is: the yard, the truck stop, or the mile marker, with the nearest exit.
• Whether it is a tractor alone or hooked to a trailer, and whether it is blocking a lane or a dock door.
• The year and make, and whether the system is 12-volt or 24-volt, if you know.

The price, and what happens next

A heavy-duty jump start for a semi truck, an 18-wheeler or another big rig is $140, plus the $19 dispatch fee charged once per job. That is a separate price from a car's jump start, which is $49–$75, so request it as a semi truck. Our average arrival is 30 minutes, and the actual time depends on the location and traffic. We text or call when the driver is on the way.

Once it is running, give the air pressure time to build before you try to move, since the spring brakes won't release until it does. Don't shut it off at the first stop. A truck that needed a jump had a reason, so have the batteries and the charging system checked.