# AGM battery charging



## Battfisher (Jan 18, 2016)

I recently bought an AGM trolling motor battery at Bass Pro. I have a Genius single bank on board charger which is supposed to be compatible with AGM, but the battery only lasts about half a trip before going dead. Could it be that the 6A charger isn't powerful enough to properly charge the battery?


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## jmrodandgun (Sep 20, 2013)

Is your AGM battery wired to the charging circuit of your outboard? If the output voltage on your outboard is 14.4v it will cook your AGM on long runs.


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## Battfisher (Jan 18, 2016)

It's not. My starting battery is not connected to the charger - the etec keeps it charged. The only load on the charger is the AGM trolling motor battery.


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## RunningOnEmpty (Jun 20, 2015)

I'm only using a 5 amp per bank onboard charger for my AGM's. So far so good.


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## jmrodandgun (Sep 20, 2013)

Have you tried to troubleshoot the charger?

Without seeing how the charger and batteries are wried, it's hard to say. Could be a parasitic loss. Could be a discharge issue.

Grab a regular 12v battery that you know is good and wire it in parallel with the AGM, regular jumper cables work fine. Then connect your trusty old bulk charger and let it charge for an hour. After an hour, check the voltage of the AGM. It should be 10.5v or better. If so, remove the jumper cables and charge away.


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## Battfisher (Jan 18, 2016)

It's a brand new charger - which I know could have issues but seems unlikely. Only things connected to AGM battery are the charger, the trolling motor receptacle, and the Garmin GPS. I don't have easy access to another 12V battery but if that's the way to check it I can pull out the starting battery and use that. Not clear on how to wire in parallel - series would be easy, but how do I split the output from my standard portable charger to have the charging cables go directly to 2 batteries?


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## Battfisher (Jan 18, 2016)

View attachment 7517
Does this mean anything as far as required amperage of charger?


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## jmrodandgun (Sep 20, 2013)

parallel is +/+ and -/-

When you give a vehicle a jump, you are wiring the two bar batteries in parallel. 

Put a meter on the AGM. If it's very low you can use the other battery to trick the charger into charging. 

https://www.optimabatteries.com/en-us/support/charging/resuscitate-deeply-discharged-battery


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## Battfisher (Jan 18, 2016)

So it appears the issue is the AH rating of the trolling motor battery, which isn't necessarily directly related to the battery group rating. Bass Pro doesn't list the AH rating like all of the other AGM battery producers do, but a couple of site recommend a minimum of a 100 AH rating. If your maximum draw at top speed is 40A, then a 100AH battery would last 2.5 hours of total draw. A 40AH battery would only last 1 hour. I bought the smallest deep cycle AGM battery that Bass Pro had, which is quite likely the reason I only get about an hour of continuous use out of that battery.


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## RunningOnEmpty (Jun 20, 2015)

Bass pro has some crazy battery prices. Check the Duracell batteries at Sam's club. They are priced right and basically a Deka intimidator agm. https://www.samsclub.com/sams/durac...rod3590232.ip?xid=plp3990105-auto:product:1:3


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## Battfisher (Jan 18, 2016)

RunningOnEmpty said:


> Bass pro has some crazy battery prices. Check the Duracell batteries at Sam's club. They are priced right and basically a Deka intimidator agm. https://www.samsclub.com/sams/durac...rod3590232.ip?xid=plp3990105-auto:product:1:3


Thanks man. I'll check them out. They appear to be a bit on the heavy side, but that may be necessary to get the higher amp hour ratings.


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## permitchaser (Aug 26, 2013)

I thought that AGMs needed 15 amps to charge


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## RunningOnEmpty (Jun 20, 2015)

permitchaser said:


> I thought that AGMs needed 15 amps to charge


This is a quote from a AGM battery manufacture, A low *amp charger* (one to 12 *amps*) is generally the best choice for *charging* any lead-acid battery. My optima blue top agm in my boat has a 10 amp maximum charge rate.


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## Battfisher (Jan 18, 2016)

RunningOnEmpty said:


> This is a quote from a AGM battery manufacture, A low *amp charger* (one to 12 *amps*) is generally the best choice for *charging* any lead-acid battery. My optima blue top agm in my boat has a 10 amp maximum charge rate.


I'm pretty sure my issue is that my AGM battery has too low of an amp hour rating, and not a problem with charging.


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## RunningOnEmpty (Jun 20, 2015)

Battfisher said:


> I'm pretty sure my issue is that my AGM battery has too low of an amp hour rating, and not a problem with charging.


I agree. How big is your boat?


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## bobber (Sep 29, 2015)

From long term practical experience an AGM should be recharged with a 12-15A capable 3 stage charger. But if your battery is too small it doesn't matter. In truth the best capacity,size,weight, and cost ratio comes from traditional wet cells, not AGMs.


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## Battfisher (Jan 18, 2016)

RunningOnEmpty said:


> I agree. How big is your boat?


My boat is 14.5', but fairly heavy. I used a Walmart deep cycle battery for years with no issues, but thought I could save a lot of weight with AGM. It appears there's not much weight savings if you get the right AH rating.


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## Battfisher (Jan 18, 2016)

bobber said:


> From long term practical experience an AGM should be recharged with a 12-15A capable 3 stage charger. But if your battery is too small it doesn't matter. In truth the best capacity,size,weight, and cost ratio comes from traditional wet cells, not AGMs.


That's interesting. What batteries would you recommend for my Salt Marsh 1444? I'll need a starting battery and a trolling motor battery.


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## wellmanj (Feb 4, 2013)

I've been using Wal-Mart Batteries on all of my boats since the 1900's. Never had issues. The last set of 3 I used for my 36V trolling motor were dated 2012. I replaced them at the end of 2017. Don't let anyone tell you they're trash. I use a Wal-Mart starting battery for starting and for a few accessories and a Wal-Mart Deep Cycle for all other needs. 
I've had a NOCO Genius 3 bank charger on my 19-6 Aquasport since 2010 and I recently bought another NOCO Genius 2 bank charger for my Carolina Skiff JV 17. I couldn't be happier with the NOCO charger. You can get them off of amazon pretty cheap: https://amzn.to/2Gm32fq. They are waterproof also.


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