99 XJR S/C won't start, compression ok

[ExecutiveTouch]

I have a 99 XJR that I've owned for 3 1/2 yrs. Usually in the cold temps and whenever the battery would get weak, it would flood out. Always before, on the advice of a Jag tech (200 miles away) that I used to work with, I would remove the plugs & coils, lay clean rags over the plug holes & turn over the engine to expel any excess fuel from the flooding, while doing so, I'd also replace the plugs. I've always noticed the compression from each cylinder by observing the rags lifting over the ports as the car is turned over. This 3rd time (yes, I'm a Glutton for Punishment, evidently), it simply refuses to fire off, it will turn over but not kick off. I've known that the catalytic converter was getting plugged, but always was able to mostly clear it while driving or before shutdown. I've always learned (and pardon the language), if it don't Fart, it won't start. Is it POSSIBLE just that the battery is simply too weak, not providing enough power either to the injectors or the coil packs, or can it be the Throttle Body sensors or Throttle body itself. Or are there any specific relays that I need to look for that could cause this behavior? I'm ALMOST at a loss for what to do, I've got a gentleman coming to buy it on Saturday as I've just Gotten quite Weary of dealing with its finicky behavior, & I'd REALLY like to make it run. These cars are NOT Cold Weather cars, & the positioning of the Battery was Really an Engineering Snafu as there is really no way to keep it warm during Extreme cold. Thank You in Advance for any Help You may be able to provide.