Originally Posted by
uwbadger
Best guess is you take Amp hours off lead acid and multiply by 0.5-0.6 to determine lithium equivalent. This is information from the LITHIUM battery companies not my own testing. Plus amp hours not a standardized number from each company either. Depends on load also. So take it ALL with a grain of salt. Using that method high quality AGM 31 lists 100 amp hours. (cheap 31 like interstate list 88 which I highly doubt). So two high quality AGM 31 should be as much or more than 1 100ah lithium. From my own experience big differences in AGM batteries. Northstar and odyssey both high quality batteries. The 2150 is 77lbs. I hated taking that in out of my boat in winter. I just highly doubt a lithium 100 will keep up with 2 high quality 31 / agm batteries in parallel. I may be wrong but my gut says two high quality 31/AGM more than one 125 lithium. 154lbs of HIGH quality lead acid vs 30-34 lbs of lithium... A $430 2150 is a lot different battery vs a $130 interstate or Sams club 31 deep cycle. But two 2150s will cost you over $800. And HEAVY. I am ordering an ionic 125 for under $1000 for my graphing. That is to cover 4 12" graphs for over 8 hrs not putting on standby, full brightness, and ducers pinging. For most a 100 would be PLENTY if just for graphing. I want the weight savings and easier on my back. I am going with 3 50's for TM (vs 27 series interstate standard with boat), 1 125 for all graphing/transducers on own wires (4 12" graphs and LS), and stock AGM for cranking battery (Merc still says use an AGM), poles, pumps, lights. Running a 2 bank and 3 bank MK precision charger. All set to AGM. Going lithium to save weight. And graphs/ducers like constant voltage. Lithiums stay higher voltage until the end. Very little drop until down to 10-20% left (depending on temperature). Plus I always run separate wire/breaker for my graphing electronics - graphs and ducer cpu boxes. Cheap solution to many potential problems. Just run some shielded 8 or 10g (depends on load and distance) to the console and bow for electronics. Not difficult. I run an 8 to each and then run 10g to each graph/cpu box. Grounding is KEY also. Need good grounds.
my 2 cents. Lithium will be a new thing for me. Electronic wiring I figured out in the past by fixing problems from major high end boat manufacturer. Now thats easy.
I may be wrong in my numbers above. I have engineering background but those numbers all I could find off internet to compare lead acid to lithium like your asking. I just dont feel comfortable with one cranking / electronics battery. Especially if one merc doesn't recommend (lithium). I can't use a 50ah lithium TM battery to jump my merc v8. Plus when your 50 miles from closest landing / civilization in Canada nice to have a battery to jump off just in case...