Starter stopped working

Thanks. Given I don't ride it but a couple times a month, wondering if a newer style l
LiFePO4 might be a better fit.

I am not sure I know enough about newer battery tech to be the one to respond on this subject. As I understand it the newer tech batteries require a range of recharge that I am not sure your older system can provide on a constant basis. I am sure there are others here who do know more about this and I hope they chime in. 

Thanks and looking at older posts it seems I'd need to update the reg/rec to one that can handle a lithium battery which eliminates the savings of those batteries being cheaper unfortunately. So maybe just a different AGM unit makes the most sense.

I also don’t think the “field coil” charging system on a 400 would give a stable enough voltage 

I do not know as some of this type of system can provide stable power, but it is very dependent upon the sense lead to the regulator and everything up stream so to speak 

What Wooky is talking about is the voltage fluctuation of old factory R/Rs.   It is said Lithium battery don't take kindly to being charged too quickly.  I went to Lithium batteries on motorcycles I own many moons ago, ..all trouble free,.... but changed factory shunt R/R to serial Shindengen SH775.......  Have rigged permanent voltmeter on bike, and factory R/R was sometimes getting uncomfortably close to 15VDC.   The SH775 keeps at 14VDC +/- 0.2 volts.   

But in this case I would confirm battery is the problem first.  I'd disconnect current battery, and hooked the one he used for cranking motor to find out. 

Old battery wouldn't take any charge at all really so I'm waiting on a new one that's supposed to get here Thursday. Will update once I've got it charged and installed.

Got the new mighty max battery, initially reader showed it was bad. So I put it on the charger for a few hours. Checked again, still said bad. Tightened up the terminals, perfect. Dropped it in the bike, starter worked 100%. So I'm just an idiot and should have tested the battery from the beginning, but now I've got a battery tester so I guess it won't happen again.

Don’t beat yourself up over it, every day is a school day and as long as you learn from the experience you’re not an idiot. If you fall in the same trap again in the future, then you will be an idiot

Exactly as Wookie stated!! Being an idiot means you didn't try. Now You've gained knowledge of the system and to Never take anything for granted. NOBODY is infallible, regardless what person's want to jam up your stovepipe. With all that free time and not having to get your fingers grimy anymore, study up on the operating principles of that VOM! I still have my old Simpson from back when i was a teenager. And Several pieces of test equipment that used Vacuum tubes ha. Have Fun!