On Board Battery Chargers

Is it OK to leave a on board charger on after the batteries show a full charge?
Especially during this cold weather, Seems like it may be good for them.
Anyone see any harm in leaving them connected?

I leave mine on all the time. It goes to stand by mode with the battery is charged.

“A 100 percent fully charged battery will not freeze until approximately minus 76 degrees Fahrenheit. A fully discharged battery can freeze at or around 32 degrees”

It's also recommended to check fluid levels at least every few weeks when a onboard charger is left on. IF fluid levels are getting close to the tops of the lead plates ... charge battery to full charge (if not already at full charge) & THEN add distilled water up to, but not into the bottom of the fill hole.

You also need to know that your charger is capable of going into "maintenance mode" before leaving it on all the time.

[QUOTE=crappiepappy;576201]You also need to know that your charger is capable of going into "maintenance mode" before leaving it on all the time.[/QUOTE]

excellent advise...this is also called float mode on some chargers. Once a battery is fully charged the charger kicks off but if you leave it plugged in it will monitor the battery and give a small charge when it detected there has been a light discharge.

Now as for leaving mine plugged in 24/7 I chose not to. Reason being I am in my garage where my boat is on a daily basis. If it's been 2-3 weeks and I have not been I will plug in my charger and top them off. Typically in the winter my charger might stay on for a couple minutes at most and then it will kick off and I unplug it.

I understand some people might store their boat where they do not have the option of being around it on a daily basis. In this case I say use your best judgment but as for me I just could not bring myself to leave my battery charger plugged in 24/7 if I was not where I could check it on a daily basis. I know there is always the story of the guy who knew a guy who had a charger to fail. I have read a post on another forum where a guy had his boat at his dad's house and it caught fire because the charger failed. His dad was at home and able to put the fire out but it did start in the bilge area where the charger was plugged in 24/7. Then there is another story where a guy went into his garage and smelled a strong sulfur odor. It was coming from his batteries. His charger had been plugged in for 3 days and did not kick off. His lead acid batteries were boiled dry and ruined. Lucky he found it before a fire started. Plus I don't like the idea of leaving a battery charger plugged in if a thunderstorm was to pop up. Again I know the instances I spoke of are 1 in a million but I eliminate the chance by simply checking my charger the next day after plugging it in and unplugging it after they are fully charged...but yes if your charger has the maintenance float mode you can leave it plugged in 24/7

[QUOTE=crappiepappy;576201]“

You also need to know that your charger is capable of going into "maintenance mode" before leaving it on all the time.[/QUOTE]

Well mine has a green light that comes on when fully charged, so is that in maintenance mode?

[QUOTE=jcclark;576203]Well mine has a green light that comes on when fully charged, so is that in maintenance mode?[/QUOTE]

Normally, yes ... but it may depend on the charger. I have a Minn-Kota 220 (2 leads @ 10a/lead) and when the lights are green it's supposed to be in "maintenance mode". On the newer "digital" or "precision" chargers, I would say definitely yes !! Mine is not "digital/precision" but the manual states : A GREEN light is lit for each bank to indicate the battery is fully charged and in maintenance mode.

I just don't leave the charger on 24/7 because the previous owner did & when I bought it from him and used it a few times & then checked the batteries, they were getting close to the fluid level being below the tops of the lead plates. He's a friend I've known since childhood & pretty meticulous in maintaining his stuff, so the only reason I can think of as to why the fluid levels were so low was that he "understood" that leaving the charger on 24/7 would keep the batteries charged/maintained at full charge ... but may not have realized that the fluid can be boiled away over time.

So why would it boil away if the charger is suppose to stop charging once charged?
Doesn't that mean the charger is overcharging.

[QUOTE=jcclark;576210]So why would it boil away if the charger is suppose to stop charging once charged?
Doesn't that mean the charger is overcharging.[/QUOTE]

Can't answer that because I'm not sure if that was the cause, or if the fluid just evaporated over time. (And I did not check the fluid levels of the batteries for some time after purchasing the boat & using the charger to charge them back up. But, I didn't & still don't leave the charger on 24/7)

As I understand it, my buddy had the boat for about a year & only used it a handful of times. The rest of the time it was in his MIL's garage & the onboard charger was on 24/7 while there.

( Google says ... Some water is lost during normal use as a consequence of the electrolysis process, and the water content in the electrolyte also tends to evaporate naturally, especially during hot weather.)

I have noticed on car batteries, when they start going bad they use water.

I did get a trickle (maintenance) charger and am going to leave that hooked up to the batteries during cold weather.
That's what was recommended to me. I was told it can extend the life of the batteries.
But the real solution is to fish more often;)

I have never had a gel, but considering it. My batteries don't have caps to open.

[QUOTE=jcclark;576203]Well mine has a green light that comes on when fully charged, so is that in maintenance mode?[/QUOTE]


Read the owner's manual to your charger and see what it says. If you don't have the owner's manual then more than likely you can go to the manufacturers website and view one.



[QUOTE=jcclark;576210]So why would it boil away if the charger is suppose to stop charging once charged?
Doesn't that mean the charger is overcharging.[/QUOTE]


If the charger fails and continues to charge then it will boil a lead acid battery dry. Eventually after enough time a charger that is stuck in full charge mode will cause a fire. As for low electrolyte levels there is a very small amount of evaporation even when everything is working correct. I typically add a small amount of DISTILLED water to my lead acid batteries about twice per year. Mine get charged about 40 or so times per year.


[QUOTE=llg;576218]I have never had a gel, but considering it. My batteries don't have caps to open.[/QUOTE]

I have a gel battery for my cranking battery and absolutely love it. Zero maintenance and it has excellent cranking amps as well as great reserve capacity. I get a lot more years out of a cranking battery than I do trolling motor batteries. I have considered going agm on trolling batteries but price is a good bit different between a AGM and lead acid battery. Plus a lead acid battery is super easy to find. Heck most people in KY are within 30-45 minutes or less of a Wal Mart that is open 24/7 so it always easy to find a wet cell trolling motor battery if you're in dire need. I don't know the real reason why but most boats run lead acid trolling motor batteries. I know of very few who run agm for trolling motor batteries...if my pocket book would allow, then I would go lithium but thats way of of the range I am willing to spend on batteries for my boat.