# Battery Question



## fishnpreacher (Jul 28, 2018)

I recharge my trolling motor battery after every trip, and I'll go ahead and top off my cranking battery when I'm finished charging the trolling battery. I had a friend tell me that I'm damaging both batteries. The trolling battery, he said, needs to be fully discharged occasionally to correct a "memory" the battery will take from not being discharged.
Secondly, according to my friend, the cranking battery stays charged by the motor. I'm "overcharging" by topping it off, even though my charger goes into maintain when a full charge is reached.
I say he is full of crap. What's the truth?


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## birdyshooter (Sep 17, 2019)

Full of it. In order to extend/optimize battery life, keep them at full charge as long as possible.


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## NealXB2003 (Jun 8, 2020)

Repeatedly completely discharging a deep cycle will shorten its life. Read up on DoD (depth of discharge). Even discharging past 50% regularly will shorten the life significantly.


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## VAFlyordie (May 7, 2021)

So, to summarize the responses, do the complete opposite of what your friend said.

No battery expert but I do what you have been doing. Recharge every time.


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## southerncannuck (Jun 27, 2016)

Lead acid batteries should be kept at full charge as much a possible.


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## Smackdaddy53 (Dec 31, 2012)

We all need a friend like this and some intelligent ones as well...


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## Mako 181 (May 1, 2020)

In over 40 years of owning boats I have never charged a starter/house battery. It / they get charged by the alternator when the engine is running.

I also run 2 batteries on a switch and never run on “both”. Either battery 1 or 2 but never both. If you are dealing with an electrical problem during the day and don’t know it you will find out when you end up with 2 dead batteries and SOL if you run them in the “both” position. 

The very first time I think my battery is low it gets replaced never charged. Also a low or weak battery will burn out a stator or power pack if you run like that.


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## Smackdaddy53 (Dec 31, 2012)

Mako 181 said:


> In over 40 years of owning boats I have never charged a starter/house battery. It / they get charged by the alternator when the engine is running.
> 
> I also run 2 batteries on a switch and never run on “both”. Either battery 1 or 2 but never both. If you are dealing with an electrical problem during the day and don’t know it you will find out when you end up with 2 dead batteries and SOL if you run them in the “both” position.
> 
> The very first time I think my battery is low it gets replaced never charged. Also a low or weak battery will burn out a stator or power pack if you run like that.


You’re tossing good batteries.


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## Mako 181 (May 1, 2020)

Naaa

don’t replace them but every 2 to 3 years. Sometimes longer. 
I use my boats and they stay charged.


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## Smackdaddy53 (Dec 31, 2012)

Mako 181 said:


> Naaa
> 
> don’t replace them but every 2 to 3 years. Sometimes longer.
> I use my boats and they stay charged.


That makes more sense.


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## southerncannuck (Jun 27, 2016)

Your friends probably thinking about the early nicad batteries found in cell phones. The would develop a memory. But that’s in the past.


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## MariettaMike (Jun 14, 2012)

fishnpreacher said:


> What's the truth?


Ni-Cad batteries were known for developing memory issues sometimes by getting recharged before being fully discharged. It is doubtful that you have Ni-Cad batteries, and I wouldn't worry about that.

It is also possible to cook a battery with a maintenance charger when the battery voltage doesn't reach the maintenance voltage trigger level. This happens when a battery is low on water and/or is near end of life. I've never had, nor used a maintenance charger for the house/starting battery in any boat I've had/have. Nor any of the cars or trucks I've had/have.

However my trolling motor batteries do go on the charger when I return, and get unplugged the next day when all the green lights are on. If all the green lights don't come on after 12+ hours I usually find I have a battery low on water, or the battery has gone bad.

If you're concerned about your house battery, maybe you should put it on the charger first. Check it in 1-2 hours to find its "topped off", and then move the charger over to your trolling motor battery and leave it there until the next trip.


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## mwolaver (Feb 6, 2014)

Without disagreeing with the above opinions, which I essentially agree with, there is some validity to what your friend says. In large, industrial or propulsion batteries, occasional full discharge and hard testing are normal activities. The navy guys talk about "moss and trees" in batteries, referring to crystaline growth between plates. These are "knocked off" by fully discharging the battery. Understand that other testing such as specific gravity of electrolyte, and other things we don't do, are occurring on these batteries. So yes, in our applications, just keep them topped off.


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## LowReynolds# (Mar 23, 2021)

There may be some other benefits to occasionally charging the starting battery. If you put the the starting battery on the charger about once a month you can determine if the battery can take a full charge. If the battery shows signs that it cannot take the full charging voltage, for me its around 13.9 volts, then potentially the battery is going bad and should be replaced soon. For me, it's really just an attempt to try and catch a bad battery before it becomes an issue. Once you charge it a few times you will see how long it normally takes and the voltage it will accept, then you'll know when something is different.


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## flytyn (Aug 21, 2012)

If my rig sits for long cold periods without running I’ll put my amp meter on the battery and if volts are below 12 I’ll top it off. Trolling motor bats I’d always recharge after use.


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## coconutgroves (Sep 23, 2013)

NealXB2003 said:


> Repeatedly completely discharging a deep cycle will shorten its life. Read up on DoD (depth of discharge). Even discharging past 50% regularly will shorten the life significantly.
> 
> View attachment 187387


This. Keep em charged. He is probably thinking of his cell phone and lithium batteries - those should be discharged to eliminate memory.

I run 24v on my center and rarely ever get below 50% even on a full weekend of fishing. I have an onboard charger with a quick connect - simply plug in to keep them full. Easy breezy.


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## fishnpreacher (Jul 28, 2018)

This friend is a smart guy, sometimes too smart for his own good....y'all know the type. I keep a close eye on my charger and batteries when hooked up. It's not on board, so I physically unhook one battery to hook up the other. 
I'll take MariettaMike's advise and charge the house battery first, that way I'll know when it's fully charged and not on "maintain." It rarely takes over 30-45 minutes to top off the house. Good advise all around, Thanks for the input.


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## hipshot (Sep 29, 2018)

I always top off the house battery after I get home. The battery is always a tiny bit off 100% when I get home, from tilting up and down and other activities associated with securing it to trailer home and putting it up in the garage. Something else to think about: Jay and I did a Port Mansfield trip where we were picking up a lot of floating grass over several days. Apparently a good bit of it found its way into the bilge. Jay got an emergency call from the plant he manages and we had to get home quick. About Kingsville we hit heavy rain. HEAVY. It lasted all the way home. When I dropped him off at the plant in Conroe (we had his truck and my boat) I noticed through the deluge that my automatic bilge pump was blowing water out of the transom. I took the boat on home and backed it into the garage, where it continued pumping for some time. The battery was way down. The loose widgeon grass had sufficiently blocked the drain that the heavy rain was backing up in the bilge. The pump was probably running constantly from Kingsville to New Caney. 
It’s cheap insurance to top off the house battery when you put the boat up. Batteries will discharge as they sit. When I got to fish every week I didn’t sweat it, but now that time on the water has gotten more elusive, I don’t want my boat sitting for weeks with the house battery even slightly discharged. The wife used to laugh at me switching my little automatic maintenance charger around between the boat, ATV, lawnmower, and the motorcycles. But our batteries lasted longer than most. Even the 7ah deer feeder battery I use for the sonar units in the kayaks gets charged after every trip, and topped off every few weeks. It’s lasted over 10 years.


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