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Battery tender dumb question

Old 08-25-2020, 03:26 AM
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Default Battery tender dumb question

My boat is stored in a storage facility that has electric access. My boat has 2 AGM batteries. I was thinking about putting a battery tender on my boat 24/7 when not in use.

Do I have to remove the battery from the boat to do so, or can I use a long extension cord and just keep the battery tender attached to the battery while it stays connected to the boat? I guess I can get 2 battery tenders or I can just rotate one between the batteries.
Old 08-25-2020, 04:26 AM
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leave connected, turn off battery switch...Look into Battery Minder vs Battery Tender

Battery Minder can handle more than 1 battery
Old 08-25-2020, 06:05 AM
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Some models of battery tender can also handle more then one battery.
Old 08-25-2020, 06:05 AM
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Or install a battery charger like a Promariner 20 or Noco Genius 2 instead of a low amp trickle one
Old 08-25-2020, 06:16 AM
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Originally Posted by LSCboater View Post
Or install a battery charger like a Promariner 20 or Noco Genius 2 instead of a low amp trickle one
This.
spend $130 and install a real 2 bank marine charger.
Old 08-25-2020, 06:32 AM
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Check with your storage facility. Some do not allow anything plugged in while you're not at the boat.
Old 08-25-2020, 06:38 AM
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id go with an on board charger as mentioned above!

its the best thing you can do for keeping your batteries happy and healthy! especially for longevity!
Old 08-25-2020, 06:46 AM
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Originally Posted by platon20 View Post
My boat is stored in a storage facility that has electric access. My boat has 2 AGM batteries. I was thinking about putting a battery tender on my boat 24/7 when not in use.

Do I have to remove the battery from the boat to do so, or can I use a long extension cord and just keep the battery tender attached to the battery while it stays connected to the boat? I guess I can get 2 battery tenders or I can just rotate one between the batteries.
You do not have to remove the battery, or batteries, from the boat. An extension cord will work just fine.

Two tenders or jumper the one tender to the other battery. It will then be charging both batteries at the same time.

Now depending upon how frequently you use the boat, you might not need an external battery charger at all. The more the boat is used the less the need for supplemental charging.
Old 08-25-2020, 06:49 AM
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Just bought a $5.99 battery tender from Harbor Freight with coupon. Buy 2 for $12 and be done with it. I checked reviews before buying since, well, it's harbor freight.
Old 08-25-2020, 06:51 AM
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i clip the cheapest battery tender 12v onto either of my 2 house batteries, & flip the battery switch to 1+2, then it charges them both

i also have a built in charger on the 2 trolling motor batteries.

one day i will install a 4 bank charger so i don't have to ghetto charge my house batteries, but hey, it works!
Old 08-25-2020, 06:58 AM
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When you return your boat to storage, your batteries are discharged to some degree. Buy a two bank smart charger and leave it permanently wired to your batteries. Maintainers are not intended for charging.
Old 08-25-2020, 07:07 AM
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Originally Posted by Inlander View Post
When you return your boat to storage, your batteries are discharged to some degree. Buy a two bank smart charger and leave it permanently wired to your batteries. Maintainers are not intended for charging.
How is that known?

For your boat? For the OP's boat? For my boat?

Never saw that with my boat. Single motor. Two batteries.
Old 08-25-2020, 07:36 AM
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Why do you need to do anything - apart from after winter layup I've never charged my batteries from anything but the engine - and there are times when I might do less than 5 miles - there have even been a few times when I've been out and done less than a mile (don't have to go far to the nearest fishing mark) so the engine is not charging the batteries anywhere near as much as a lot of people but they're fine.
Old 08-25-2020, 07:39 AM
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Originally Posted by platon20 View Post
My boat is stored in a storage facility that has electric access. My boat has 2 AGM batteries. I was thinking about putting a battery tender on my boat 24/7 when not in use.
Our AGMs didn't really self-discharge very much over time. I took our generator battery off the charger, never needed to mess with it. I never had to charge our main engine/house batteries over a winter storage. I haven't ever used a "tender" on my tractor's AGM start battery.

-Chris
Old 08-25-2020, 07:40 AM
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Originally Posted by alloyboy View Post
How is that known?

For your boat? For the OP's boat? For my boat?

Never saw that with my boat. Single motor. Two batteries.
You will never get a battery that's in use and simultaneously being charged fully through the absorption stage of charging. Is it absolutely necessary to do so.....no, but it is best practice if you have the option. Particularly if you are trying to maximize battery life on an application where the batteries sit without for use for any length of time. If it is being frequently used, as in weekly at least, there is little benefit. Batteries that sit around last longer when allowed to fully charge through he absorption stage to completion.
Old 08-25-2020, 07:51 AM
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Originally Posted by autobaun70 View Post
You will never get a battery that's in use and simultaneously being charged fully through the absorption stage of charging. Is it absolutely necessary to do so.....no, but it is best practice if you have the option. Particularly if you are trying to maximize battery life on an application where the batteries sit without for use for any length of time. If it is being frequently used, as in weekly at least, there is little benefit. Batteries that sit around last longer when allowed to fully charge through he absorption stage to completion.
Absolutely correct.

Batteries discharge from use. It is virtually impossible for a motor alternator to bring batteries up to full charge because the absorption phase alone takes a minimum of 7 hours.

Many boaters cannot charge while their boat is stored and it serves them well enough. They dont have a choice. However, if a choice is available why wouldn’t you charge? Not only does a partially charge battery have reduced capacity for subsequent use, but if left chronically partially charged, battery life is substantially reduced. It pays to use a smart charger.
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Old 08-25-2020, 07:56 AM
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Originally Posted by autobaun70 View Post
You will never get a battery that's in use and simultaneously being charged fully through the absorption stage of charging..
So you imagine that electricity can "simultaneously" both leave, and enter, a battery?
Old 08-25-2020, 08:26 AM
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Originally Posted by Fwpratt View Post
So you imagine that electricity can "simultaneously" both leave, and enter, a battery?
Where have you been?

They are working on the other site.
Old 08-25-2020, 08:33 AM
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I will be 72 next month. Owned cars, trucks, boats and airplanes along the way since 16.

Must have had incredibly good luck. Nothing but dumb constant voltage generators, alternatives and PMGs in use. Batteries all worked just fine.

Now it seems to be the kiss of death if an exotic and smart charger is not used. Have the batteries changed?
Old 08-25-2020, 08:41 AM
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I purchased 2 solar 7.5 watt solar chargers from home depot at $50.00 each. Keeps 4 batteries fully charged.

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