Most generator failures aren't engine failures. After reviewing over 200 generator units a year as a quality manager, I can tell you the three most common reasons a new generator disappoints are under-sized starting wattage, fuel that's gone bad, and a 12-volt battery that hasn't been checked since the last outage. The engine is rarely the weak link—the support systems are.
I work on the B2B side, which means I'm not choosing a generator for a weekend cabin; I'm approving equipment for installers, distributors, and commercial clients who will lose real money if the unit doesn't start when it matters. That changes what I look at. I don't care if a generator looks good in a brochure. I care whether it will start under load, whether the oil filter is going to survive a cold start, and whether the battery can turn the engine over when the grid is down.
Here's what I've learned from a decade of doing this—and from rejecting more first deliveries than I can count.
Starting watts vs. running watts: most buyers get this wrong
Take the Briggs & Stratton Storm Responder line. The 5500-watt unit is a solid choice for many homes, but I keep seeing spec sheets that list '5500 watts' as if that answered everything. In reality, the 5550-watt model in that series has 8550 starting watts. That number is what matters when your refrigerator compressor kicks in, your furnace blower spins up, or your well pump starts drawing water.
The typical buyer looks at running watts and assumes it's enough. The question they should ask is: what loads will this generator start? An electric motor can draw two to three times its running wattage for 0.1 to 0.5 seconds during startup. A 5,000-watt well pump might need 12,000 watts to get moving. If you size by running watts alone, you'll be sitting in the dark with a generator that hums along but can't handle the surge.
(Should mention: we always factor in a 20% derating for altitude and another 15% for temperature extremes. Most spec sheets are measured at sea level and 72°F. A generator rated at 5,500 watts at sea level will deliver considerably less at 5,000 feet in January.)
In our Q1 2024 quality audit, we rejected a batch of portable generators because the starting wattage was printed in tiny type while the running wattage was plastered across the box. That's not an engine problem—it's an honesty problem. A generator that can't start your motor is a paperweight, no matter how well it runs.
Diesel vs. dual fuel: a matter of certainty
I get asked about Generac's home diesel generator at least once a month. And for good reason: diesel is the right answer for a lot of commercial sites. Diesel doesn't degrade as quickly as gasoline, and diesel engines are typically built for longer runtimes. If you have a site with critical loads, a Generac diesel unit can be a workhorse.
But for emergency backup at a house or small business, I usually prefer a dual-fuel generator—gasoline or propane. Propane stores indefinitely, and that's a big advantage when the timeline is uncertain. Gasoline can go bad in as little as 30-60 days (depending on ethanol content), and that's a common reason portable generators won't start after a few months of sitting idle.
People think diesel generators are inherently more reliable because they're built heavier. Actually, the causality runs the other way: diesel generators are usually run harder and over longer periods, so manufacturers build them heavier. If you're using a generator for a few hours a day during occasional outages, that extra weight doesn't buy you much. A dual-fuel portable unit is often more practical for a residential install, and it gives you a fuel insurance policy.
That said, if you have a critical load—say, a small business with refrigerated inventory—the longer runtime of diesel on a single refueling is a genuine advantage. I once saw a Generac diesel unit carry a small cold-storage room through a five-day outage without a hiccup. The owner didn't have to worry about refueling every 8 hours, which is exactly what you want when roads are closed.
Oil filters: the cheapest insurance (or the most annoying failure)
When I inspect a generator, I always check what oil filter is specified. For many Briggs & Stratton engines, the G35 oil filter is standard. It's a spin-on filter that costs a few dollars. But I've seen aftermarket filters with bypass valves that open too early, or filter media that collapses under cold-start pressure. They fit, but they can starve the engine at the worst possible moment.
We ran a blind test back in 2022 with identical generators using a genuine G35 versus a budget no-name filter. The budget filter caused a 3-4 psi oil pressure drop at idle. The cost difference was about $4 per filter. On a 10,000-unit run, that's $40,000 to potentially damage every engine. That's a false economy. Now every contract we write specifies the OE filter.
(I should add: I've never fully understood why anyone would risk a warranty claim over a $4 part. If someone has insight, I'd love to hear it.)
How to test a 12-volt battery with a multimeter (do this before the storm)
One of the simplest checks is also the one most people skip. Here's how to test a 12-volt battery with a multimeter: set the multimeter to DC volts, touch the red lead to the positive terminal and the black lead to the negative terminal, and read the voltage. A fully charged battery should show around 12.6 volts. At 12.4 volts, it's about 75% charged. Below 12.2 volts, the battery is weak and may not crank the generator when the pressure's on.
The caveat: open-circuit voltage doesn't measure cranking amps. A battery can read 12.7 volts and still fail under load. For a better check, use a load tester. But if you're in the field and haven't touched the battery in six months, a multimeter reading is a fast way to catch problems that are already visible.
I also check if the battery has a maintenance charger connected. A generator that sits for months with a lead-acid battery at partial charge will develop sulfate on the plates, which reduces capacity. A smart maintainer isn't expensive, and it buys you certainty. In March 2024, we paid $400 extra for rush delivery on a replacement battery for a client's standby unit. The alternative was missing an $18,000 event the next day. That's the time-certainty premium: you're not paying for the part; you're paying for the certainty that the generator starts when you need it.
When to ignore all of this
There's no perfect generator. If you're in a region with short, infrequent outages, a budget portable might be good enough. If you're installing for a commercial client who will lose money on every hour of downtime, pay for the diesel standby and spend the money on an ATS (automatic transfer switch) that's sized correctly. I've seen more than one business spend $10,000 on a generator and then discover the transfer switch couldn't handle the load.
The other thing I'd say is: don't buy a generator purely on brand loyalty. Briggs & Stratton makes excellent units in the Storm Responder line, but the best generator for you depends on your outage pattern, your fuel storage, and the loads you actually need to run. As of January 2025, the market is still shifting toward inverter generators for noise-sensitive areas, but for raw starting muscle, the traditional brushless units remain the workhorses. Verify current specs at briggsandstratton.com or your local distributor before ordering—generator lines change more often than you'd think.
If you're in a hurry, at least remember this: check starting watts, verify the fuel, change the G35 oil filter on schedule, and test that 12-volt battery now—not after the storm arrives.