# On-board vs Tender charger.



## Redman1776 (Jul 14, 2014)

I am not an electrician by any means so please be gentle if this is a stupid question.
What is the difference between buying a $120+ on board charger or using a $20 battery charger/tender for each battery? I have to run an extension cord to the boat either way.


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## Misdirection (Jul 16, 2012)

The battery tender is probably only 1 amp, a charger is probably 6 amp. An onboard charger probably has 6 amps per battery. So for the tender, if you needed to use your tolling batteries the next day, they might not be full charged. As far as a charger vs an onboard charger, convenience of only having to plug one charger in vs multiple...


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## Riverduck11 (Jul 11, 2013)

I am not an electrician either, but life is a lot easier with an on board charger. After about 2 weeks carrying the charger around to each battery and hoping to get all charged before I go back out, I got a 3 bank Minn Kota for like $140 with a rebate. Life is much easier and I honestly think I got better performance from my batteries.


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## lonewolf (Mar 4, 2010)

A tender just has enough amperage to keep a battery at full charge. The on-board will have enough amperage to charge the batteries after you have fished all day. Most are at least 5 amps . One that says 10 has two 5 amp leads


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## Redman1776 (Jul 14, 2014)

The charger/maintainers I bought are 1.5 amp. I usually recharge my batteries using a single charger on the 2 amp setting one battery at a time after carrying them from the boat to the garage. 
I have to run an extension cord to the boat whether I spend another $100+ and I can leave the cords attached to the batteries with the charger/maintainers and plug them in when I run the cord. Next question is if I have a 24 volt bank will that disrupt the single 12 volt charger to each battery?


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## sixtyminutes (Jan 3, 2009)

Recharging deep cycle batteries should be done as quickly as possible. My electronically controlled and fully automatic charger throws 30 amps at the batteries for the first part of the recharging cycle. The amps gradually are reduced as the battery nears full charge. Once fully charged it maintains the battery. The battery tender is designed to maintain a full charge without cooking the battery. Charging deep cycle batteries with a trickle charger will seriously shorten the life of your batteries. My buddy who is an electrical engineer could explain it to you but just do some research on deep cycle batteries. You can use a 12 volt charger even if you have the batteries wired for 24 volt output. A good onboard charger recharges with high amps and then switches to a low amp maintenance charge. You can keep them on charge all the time and you never need to remove them from the boat. I have onboard style for my boat but I use a lot of batteries for other purposes. I get about 7-8 years out of my trolling motor batteries.


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## Redman1776 (Jul 14, 2014)

sixtyminutes said:


> Recharging deep cycle batteries should be done as quickly as possible. My electronically controlled and fully automatic charger throws 30 amps at the batteries for the first part of the recharging cycle. The amps gradually are reduced as the battery nears full charge. Once fully charged it maintains the battery. The battery tender is designed to maintain a full charge without cooking the battery. Charging deep cycle batteries with a trickle charger will seriously shorten the life of your batteries. My buddy who is an electrical engineer could explain it to you but just do some research on deep cycle batteries. You can use a 12 volt charger even if you have the batteries wired for 24 volt output. A good onboard charger recharges with high amps and then switches to a low amp maintenance charge. You can keep them on charge all the time and you never need to remove them from the boat. I have onboard style for my boat but I use a lot of batteries for other purposes. I get about 7-8 years out of my trolling motor batteries.


Thanks for the tip. That's opposite of anything I've ever been told, I guess I've never researched it myself. I was always told a slow recharge is best.


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## sherman51 (Apr 12, 2011)

the charger I have is fully automatic. it charges 4 amp 20 amp and 40 amp but I can set it for 40 amps and it may only charge 30 amps depending on what the battery will take. and as the battery gets charged the amps drop until the battery is charged then shuts off until the amps in the battery drops then the charger kicks back on and charges until full again. I do charge my batteries 1 at a time but I've never failed to have fully charged batteries for a fishing trip. and I also use my charger for charging my rv starting battery and 2 house batteries when its stored for awhile. I charge my batteries every couple of months and they last for yrs.
sherman


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## leeabu (Apr 10, 2004)

Redman1776 said:


> Thanks for the tip. That's opposite of anything I've ever been told, I guess I've never researched it myself. I was always told a slow recharge is best.


Find the a/h rate of your battery and divide it by 8. This is the amp charger you need. This allows the battery to fully charge in no more than 8 hours. Charging at a higher rate can cause too much heat in the battery which can damage the plates. The battery should also have enough time to cool down after the charge before use.;


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## saugmon (Jun 14, 2006)

If your boat was set up like mine redman,an onboard charger is a must. My starter battery is under the rear deck with the oil tank in front of it.Hard to get battery cables back there.The rear deck has to come off to replace that battery.Got both wired in with a 5/5 motorguide charger that is over 14 yrs old and going strong.


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## Redman1776 (Jul 14, 2014)

My boat currently on order (hopefully here soon) has the battery storage beneath the center rod holder. Other than being a pain reaching down to lift the battery from the bottom of the boat it's fairly convenient. I've decided though that they are only being removed for winter storage. Cabela's has their on board charger on sale for $90 right now I may look into that after all of the suggestions being against my cheaper charger/tender idea.


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