so what i have learned, ... the batteries are not necessarily that much lighter in weight, they might be more in the 50% weight reduction range. also, there are many forms of lithium batteries. you probably would want to look at lithium iron phosphate battery (LiFePO 4 battery) or LFP battery. easiest to get into.
Genuine Lithium Batteries for DIY Projects – Battery Hookup
USED HEADWAY 38120 HP 3.2V 8AH LIFEPO4 BATTERY – Battery Hookup
Genuine Lithium Batteries for DIY Projects – Battery Hookup
USED HEADWAY 38120 HP 3.2V 8AH LIFEPO4 BATTERY – Battery Hookup
this is a really good question. i have not really seen a lot of info/data on this question. i picked up some of the headway cells, i'm in process of putting a pack together to test out. but a lot of guys have used this them successfully from my understanding. this is a maybe a complicated question, i suspect. some of the lithium batteries are rated based on alternator charging capability. you have probably seen that already.