Lithium Ion or Lithium Iron Battery for a 1977 KZ650B

Any suggestions?

I have Dyna S ignition in the bike, if that matters.

Have no idea why i keep having to add acid to this damn battery I have in (yuasa AGM)

If you must add water to your battery very frequently rather than just occasionally your bike's charging system may be overcharging the battery. If that is the case, changing to a Lithium based battery may be a bad idea unless you correct he charging problem. I strongly suggest you check the bike's charging system before changing the battery. Ed

In addition to what Ed said you should never add acid to any battery, other than when brand new maybe. Distilled water is what should be added if the level is low. Seems strange to add anything to an AGM battery though since the fluid is absorbed into the glass mat material.

Regarding a new battery, AGM batteries are good...for the most part. I just ordered a new one for my 750 this morning since the old one took a dump. Sat too long discharged. My bad.

I used a lithium battery for a while, it worked well.

But 650Dude is probably right - it may be overcharging. I checked the charging system on my bike, and it sat at around 14.4V - a little high but pretty normal for an older bike. But when turning the headlight on it went up over 15V. This is because the regulator rectifier on my model uses the accessories circuit as a baseline for the charge - so when the accessories were under load, the voltage on the accessories circuit would drop and the regulator would increase the voltage to make up for it, and increase it too much for the battery.

Cleaning all your terminals and using relays for the headlight will fix this issue if you have it.

My 18 year old ZRX is on its second battery, both Yuasa AGMs. Never needed to add a drop to either of them.
Like the other folks have said, overcharging is the most common culprit.