I'm having some troubles starting a Buick regal, '98 3.8L.
I've replaced the starter, charged the battery, and checked all the fusses.
The car won't respond to a boost at all, and a neighbours diagnostic tool was drained dead when the car is in the bulb check/ start position. Anyone have any suggestions?

This link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post235560

Try load testing the battery; otherwise, just install a new battery. There may be an internal problem with the battery.

Could it be a problem with the ignition or alternator? A bad relay somewhere? If it was a bad battery, would the car not respond to a boost?

Yes, there can always be a problem with an ignition switch, corroded cables, etc. There could also be a major internal problem with the battery, where the impedance is extremely high, possibly infinite. Then, your booster won't help. When you placed the battery on the charger, did the ammeter cut back to around 1 amp?

Did you closely examine the battery cables for internal damage? Ensure the main ground is clean. Test all under hood and under dash fuses with a test light or multimeter--visual inspection is not good enough!

If you perform the steps on the link I provided, you will find the problem.

I've got a buddy coming over with a voltmeter and ammeter. I want to trouble shoot as much as possible, I'm just hoping it's nothing to do with the ECM. :(
There is a recall for the ignition on that model, how do I check to see if this car was?

The ECM should not prevent the starter motor from working. You can call your local Buick dealer concerning any TSBs.

I printed it off already... Hoping sort it out before dark. Thanks for the help, I'll let you know if it works.

One last question, can I swap a relay from... say the air conditioning for the starter relay instead of going and buying a new one?

No.

I can't locate the main ground on the engine block either. I want to clean it and check for corrosion.