Thread: Rookie Question

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  1. #1
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    Rookie Question

    How would two high quality AGM's (Northstar group 31's) ran in parallel compare to a 100 amp hour lithium? Running another thread on house battery setup, charging, etc. but my entire problem would be solved if two Northstars would be equal to one Lithium. The specs on the two are different, and I want to make sure I don't misinterpret. I hate the added weight, 40 lb's or so is not the end of the world, but I'd give up some there if the two quality AGM's would be strong enough, plus they'd charge easier both on land and of the alternator.

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    #2
    Well, from what I have been reading the cost difference between two Northstars and one Lithium is negligible.

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    #3
    Yes, all things being equal, I'd go lithium in a heartbeat. But, Merc requiring AGM's is messing up my plan for that :(.

    Quote Originally Posted by billnorman1 View Post
    Well, from what I have been reading the cost difference between two Northstars and one Lithium is negligible.

  4. Member
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    #4
    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...
    Last edited by uwbadger; 10-23-2020 at 08:43 AM.

  5. Member
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    #5
    Thank you badger....I'm almost ready to go with parallel AGM's, ONLY because Merc requires one for cranking. I'd only get 40 lb. weight savings if I went AGM crank/Lithium house. Plus, I could go either way on trollers, but with the new chargers, those can get charged on the water too. Might just be simpler going all AGM. It is an additional couple hundred pounds, that I'd rather do without, but for charging and simplicity, all AGM (good ones) might be my best bet.

    Quote Originally Posted by uwbadger View Post
    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...

  6. Member
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    #6
    To me its a ? of weight. nobody is running down 3 good quality agm 31 trolling motor batteries in one day...

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    #7
    Definitely not running them down with the new chargers that'll charge trollers on the water. That's why I may go AGM's. I'd love to shed the 200 lbs and pick up a few mph's, but for the sake of simplicity I may go the agm route. All this is due to the Merc requirement, or it would lithiums all around no doubt. Oh well, I'll see what dealer comes back with on the lithium setup, maybe they have a better idea than me.
    Last edited by TohoRookie; 10-23-2020 at 09:52 AM.

  8. Member
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    #8
    I am just running 4 lithiums and one AGM. MK chargers use AGM setting to charge lithiums.

  9. Member
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    #9
    Couple other questions. On the lithiums, for charging can you just leave them going? I keep my boat at storage and they charge it there. Second question, what does your outboard alternator charge? Just the cranker?


    Quote Originally Posted by uwbadger View Post
    I am just running 4 lithiums and one AGM. MK chargers use AGM setting to charge lithiums.

  10. Member
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    #10
    FWIW I have been using the 100 ah Ionic for a starter battery on my 115 hp merc 4s for over a year now with no issues..always charged when I get back to launch and haven't put a charger on it since my initial charge. Many guys with merc SHO's are using them and haven't seen issues crop up from those users as well. Super nice to have the app to keep up with battery status not to mention the weight loss...(I have 3 other Ionics on my boat).