Batteries get ignored until the morning a diesel will not crank. Then they are all anyone can think about. A diesel’s batteries do heavier work than a gas engine’s, and Florida heat shortens their lives. RDI Power tests and replaces batteries at our Brooksville shop for owners and fleets throughout Hernando, Pasco and Citrus counties.
How diesels use batteries
- Diesel pickups from Ford, Ram and GM carry 2 batteries wired in parallel to feed the starter and the glow plug or intake heater circuit.
- Heavy trucks commonly carry 3 or 4 batteries, often Group 31, in a battery box on the frame.
- Buses and RVs add separate house or coach batteries for lighting and accessories.
- Work trucks with lift gates, inverters and emergency lighting add load that the batteries carry whenever the engine is off.
Heat, not cold, is the real enemy
Cold weather gets blamed for dead batteries, but heat does most of the damage. High temperatures speed up corrosion of the internal plates and evaporation of electrolyte. A battery cooked all summer often has just enough left to start on warm days, then fails the first cool morning in January.
How we test batteries
- Visual check: case swelling, leaks, terminal corrosion, loose hold-downs.
- State of charge: a discharged battery has to be charged before it can be tested fairly.
- Conductance or load test: measures the battery’s ability to deliver cranking current, compared to its rating.
- Each battery separately: in a multi-battery bank, a single failed battery can hide behind the others and drag the whole bank down.
- Charging and drain checks: a battery that keeps dying may be the victim, not the cause. We check alternator output and measure key-off draw.
Replacing batteries the right way
- Replace batteries in a bank as a matched set: same type, same rating, same age.
- Clean or replace corroded terminals and cables; corrosion adds resistance the starter will feel.
- Secure hold-downs, since vibration kills batteries early.
- Choose the type the vehicle calls for, flooded or AGM, and the cold cranking rating it needs.
Parasitic drains
Telematics units, ELDs, aftermarket lighting, stereo amplifiers, inverters and modules that fail to go to sleep can all pull power with the key off. On a truck that sits over a weekend, or an RV in storage, a small draw adds up to a dead bank. We measure the draw, pull fuses to isolate the circuit and trace the cause through our electrical repair process.
Vehicles that sit
Diesel pusher motorhomes, seasonal equipment trucks and spare fleet units sit for weeks. A battery disconnect or a maintainer keeps the bank healthy between trips; letting batteries go flat repeatedly shortens their lives. We can check RV batteries as part of RV service.
Fleet battery checks
On fleets, battery testing belongs in every preventive maintenance visit. Catching a weak battery in the shop costs far less than a no-start at a job site. RDI Fleet plans include it.
If the engine cranks slower than it used to, or the batteries are more than a few summers old, bring the truck in for a test. Starting complaints beyond the batteries are covered on our starter repair page.