TL;DR: It takes approximately 2.5 minutes of focused fire (with Budda's hypothetical 15-ceptor gankfleet) to break a standard AFK-fit Rattler, not counting any time spent shooting drones - be very careful of what reinforcements such a ship can call in. If it's a bait Rattler, gtfo because you're going to welp your entire fleet. (You know it's a bait Rattler if anybody in your fleet gets neuted or grappled; some PvE Rattlers still fit rapid heavies so that's not a reliable indicator.)
Background and fits:
Nullsec ratting Rattlers vary quite a bit depending on how at-the-keyboard the pilot wants to play them, and whether the pilot wants to be pvp bait or just maximize site clearing times. Here are a couple sample fits; they're designed for using in the drone lands but would work equally well in Angels/Serp/Gurista space (would need changes in EM/therm ratting areas).
Afk rattle:
[Rattlesnake, drone rat active cheap]
Federation Navy Drone Damage Amplifier
Federation Navy Drone Damage Amplifier
Federation Navy Drone Damage Amplifier
Damage Control II
Ballistic Control System II
Capacitor Flux Coil II
Adaptive Invulnerability Field II
Shield Boost Amplifier II
Republic Fleet Large Cap Battery
Adaptive Invulnerability Field II
Pith X-Type Large Shield Booster
100MN Afterburner II
Shield Boost Amplifier II
Cruise Missile Launcher II, Inferno Precision Cruise Missile
Cruise Missile Launcher II, Inferno Precision Cruise Missile
Cruise Missile Launcher II, Inferno Precision Cruise Missile
Cruise Missile Launcher II, Inferno Precision Cruise Missile
Cruise Missile Launcher II, Inferno Precision Cruise Missile
Drone Link Augmentor II
Large Core Defense Capacitor Safeguard II
Large Core Defense Capacitor Safeguard II
Large Capacitor Control Circuit II
Praetor II x2
Acolyte II x5
Praetor II x2
Gecko x1
Tanks ~850ehp/s cold, cap stable. Heated tank ~1250ehp/s, lasts over 15 minutes. Damage doesn't apply well to combat ceptors, but this fit is designed to tank while the pilot yells for support.
Bait rattle:
[Rattlesnake, bait]
Damage Control II
Drone Damage Amplifier II
Drone Damage Amplifier II
Drone Damage Amplifier II
Sentient Omnidirectional Tracking Enhancer
Ballistic Control System II
Large Micro Jump Drive
Gist C-Type X-Large Shield Booster
Adaptive Invulnerability Field II
Republic Fleet Large Cap Battery
Heavy Stasis Grappler II
Warp Disruptor II
Heavy Capacitor Booster II, Navy Cap Booster 800
Rapid Heavy Missile Launcher II, Caldari Navy Inferno Heavy Missile
Rapid Heavy Missile Launcher II, Caldari Navy Inferno Heavy Missile
Rapid Heavy Missile Launcher II, Caldari Navy Inferno Heavy Missile
Rapid Heavy Missile Launcher II, Caldari Navy Inferno Heavy Missile
Rapid Heavy Missile Launcher II, Caldari Navy Inferno Heavy Missile
Heavy Energy Neutralizer II
Large Core Defense Capacitor Safeguard II
Large Anti-EM Screen Reinforcer II
Large Anti-Thermal Screen Reinforcer II
Praetor II x2
Curator II x2
Caldari Navy Inferno Heavy Assault Missile x1000
Navy Cap Booster 800 x25
This tanks considerably less than the afk fit, because it's designed to sit 100km off the warp-in and blap rats with sentries. The drone DPS is comparable to an Ishtar by itself, so the missiles can be reserved for clearing annoying frigate spawns and for actual PvP. Heated tank is around 700ehp/s.
Analysis:
While the "AFK Rattler" isn't particularly fearsome by itself vs. combat ceptors, note that it's got around 115k-127k ehp (depending on heated invulns) + the reps. So if you have 2k dps, your effective dps (your applied dps - the target's reps) is around 800. Assuming heat issues will prevent continuous overheating of invuls, we can say that the ehp end up around 120k. This means you will have to be shooting for a minimum of 150 seconds to break the rattler, plus any time you spend shooting drones instead of the Rattler (if you go back and forth, note that the Rattler will of course be repairing heat damage and boosting shields anytime you shoot the drones, partially resetting your kill timer).
An example:
Eventually, if not supported, the Rattler will eventually die; if you're very conscientious about clearing drones and warping out to a ping when yellowboxed, you can get the kill with basically no losses. However, it's still pretty risky, and not just because the Rattler's 7kish volley can delete ceptors that get dumb. Consider the following
killfeed, which happened when I was running a 10/10 and bumped off a structure while aligning to a safe just as the Curses warped in. The hostile gang was optimized to hunt down and kill 10/10 runners; they put Natasha's Curse in system with a "clean" (i.e. doesn't appear on killboards) alt in a Helios, then put out combats. Since the Curse doesn't appear on dscan and the hostile combats mean that warping to a safe can get you scanned down without the benefit of acceleration gates, site runners will often align to a station and try to get an alt in to ensure that there are no bubbles anchored on the station grid. Once you get the Curse in and land a point, the two Curses can neut out the site runner, the Sabre bubbles, and they bring in the Mach as quickly as possible for additional DPS.
But here's the thing: With just drone DPS and cruise launchers, I killed one of the Curses and the Sabre, and the other Curse had to warp out in <20% structure. Had I not flown like a panicked muppet and burned out my launchers, I would have killed
both Curses and either killed the Sabre or forced it off grid, and then likely warped away to safety. And that's against a gang that can actually shut down a Rattler's tank.
Now that you've learned how to calculate your DPS vs their DPS, let's look at the PvP-fit Rattler. On the one hand, it tanks less raw dps than the PvE version, because fewer midslots are devoted to tank; its cold tank is 106k ehp buffer with 505ehp/s reps; hot tank is 111k ehp buffer with 709 ehp/s reps. On the other hand, it has a
lot of cap booster charges, can neut out a ceptor's entire cap in one neut cycle, and can grapple and point things. If you get grappled and neuted by this thing in a ceptor, you. Will. Die. In fact, while your 15-ceptor gang can break through reps and kill the Rattler in only 85 seconds, that comparison of outgoing DPS versus target reps misses a crucial fact: the Rattler is going to mow through your ceptor gang at the rate of approximately one ceptor every five or six seconds, which means your outgoing DPS is a linear function steadily approaching zero rather than a constant. (Realistically, the Rattler's main constraint in killing your ceptors is lock speed; even if the pilot immediately delocks all rats and starts locking you when you land on grid, it still takes some few seconds to lock up ceptors with a battleship and you'll get a head start where "only" drone DPS is incoming.)
An example:
About a year ago, I grabbed some NSC folks and went on a roam through a WH connection to Delve. (This was before the Imperium had occupied Delve.) The AAR can be found
here, and the relevant killfeed is
here. What you need to know for background is that the fleet was approximately 15 ships, with DPS in T3Ds and assault frigates, and with 3 shield logi frigates. In other words, it was much better suited to actually fighting on grid than a combat ceptor fleet. And we got roflstomped through logi reps.
Don't fight bait Rattlers, kids.
A Coda:
The fits above are basically reasonable baseline fits, the cost of which a pilot could reasonably hope to recoup over the life of the ship. (For example, the "AFK" cruise fit makes its cost back after 4-5 successful drone 10/10s.) But what if someone had a lot of ISK, liked to bait out fights and then
bravely take on the blob have a cyno alt and a carrier or FAX on standby, and in short was maybe a little bit of a jerk?
(Not shown: Still using cheap T2 Praetors because they track better than a Gecko; using Antipharmakon Thureo to increase shield reps without booster drawbacks; cloaky cyno linksrepgu [links not currently applied]; cap alts.)