Battery Charging Compatibility

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717
Location
Chatham, Ontario, Canada
Thread starter
This is a marine application but I thought I might get more reads and knowledge if I put it here. The Interstate group 27 deep cycle battery in my boat called it quits last fall. It didn't owe me a thing as i have had it for eight years. I purchased an AGM replacement for it yesterday and put it on the charger prior to installing it in the boat. After careful thought I wonder if I made a wise choice. My starting battery is a regular lead battery. I have an on board smart battery charger that connects to both batteries and is tuned on whenever I am not on the boat. Is it wise to have two different battery types on the same onboard charger and would each be fully charged?
 
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24,816
Location
Upstate NY
I guess the question is does/can the charger treat each battery separately? Each with its own charging characteristics. I guess you need to read the smart charger directions.
 
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24,816
Location
Upstate NY
Originally Posted by cb450sc
I purchased the boat used. No manual included.
Then you need to get the make/model and track down a manual or email the manufacturer.
 
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2,072
Location
America's Dairyland
CTEK says it ok as long as the Ah of the batteries is within the capacity range of the charger. I say that it would be a compromise for the AGM since it likes a higher charging voltage vs. lead-acid. Chargers aren't that expensive and a good one can last a lifetime so why not pick up another. You'll stimulate the economy at the same time!
 
Messages
717
Location
Chatham, Ontario, Canada
Thread starter
I found an online manual and it says that the onboard charger charges the batteries separately according to each batteries state of charge. I guess this would answer my own question. Thanks for taking the time.
 
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8,094
Location
New England
What voltage does it charge the battery at? AGM batteries like to be charged at a slightly higher voltage than flooded LA batteries; however, they're more prone sensitive to over-charging. If you gas an AGM to the point where the reliefs lift, that electrolyte is gone forever. I wouldn't say this is a problem while operating the motors to charge an AGM battery, but the trickle charger may maintain too high of a voltage for too long or not maintain a high enough charge long enough to fully charge it.
 

JHZR2

Staff member
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44,497
Location
New Jersey
Is there a switch to change between batteries? If you're charging, make sure they're isolated from one another. Not only will the capacity, state of health, impedances, etc. vary, but the appropriate charge voltage and behaviors are different. So it's best to charge independently. If they're wired in parallel based upon switch position, you just need to be careful.
 
Messages
24,816
Location
Upstate NY
Originally Posted by cb450sc
I found an online manual and it says that the onboard charger charges the batteries separately according to each batteries state of charge. I guess this would answer my own question. Thanks for taking the time.
Does the manual for the charger say anything about AGM batteries?
 
Messages
24,816
Location
Upstate NY
remember if you do any replacement of the charger it needs to be a marine one and listed for use in engine bay if that is where its located.
 
Messages
959
Location
Arizona
IMO it depends on how Smart the charger is. Newest ones have strong analysis mode of the attached cells and apply just the right amount of current/rate to fill them up without damage. Charging different battery types in parallel would defeat the smart part of the charger.
 
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2,411
Location
Deep in the heart of Jersey
If your trying to keep both charged and they are wired to charge together, the charge level in both, will only reach the capacity of the weakest battery. The newer battery will be less, then what it could be if charged separately. If you can charge them separately, that's what I would do.,,
 
Messages
717
Location
Chatham, Ontario, Canada
Thread starter
Just a follow up. I installed the battery and connected it to the charger. There are separate red/green lights for both batteries. Both came up green, fully charged, so I think I will be fine. I also emailed,ed the manufacturer. They said it charge each battery separately. Thanks for everyone's comments.
 
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