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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 11-04-2008
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Using a portable battery charger onboard

I got this portable battery charger from West Marine to charge the deep cycle / starting batteries (a pair of Walmart-brand 12V cells, model no. "24-DC", 75 Ah each) on my boat. I got it instead of the $10-more-expensive "onboard charger", not knowing that the instructions said that a marine battery must be removed from the boat and charged onshore.

What's the reason for this requirement? I figure if the 6A alternator on my outboard is okay to use on the boat, why not a 6A charger? Is it because there's a power cable running from shore or something?

So the first time I used it, I lugged the batteries to shore. Egads, were they heavier than I expected. Also they are not stowed in super-accessible locations (like, under the v-berth). I really really want to just attach the alligator clamps to the terminals in the engine compartment. Will Ι create any micro black holes if I do this?
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Old 11-04-2008
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I would say the danger would be from leaving it in a gasoline powered boats engine compartment WHICH would require and ignition safe charge


If your just charging a battery on a boat i am not seeing the danger
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Old 11-04-2008
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Adam-

Which battery charger did you get? Is it an intelligent three-stage charger? If not, it will probably likely fry your batteries...

Most portable battery chargers aren't recommended for use on a boat as they can be a fire hazard. The alligator clips can come loose unexpectedly, and that can be bad. Also, it requires you to open the battery box to have the clips attach to the battery posts, and if you leave the battery box open and something falls across the posts...bad things can happen.

If you want to charge the batteries on the boat, you're much better off hardwiring in a proper marine battery charger into the system.
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Old 11-04-2008
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Battery Caharging on board

In addition to the dangers of heavier than air volotile gases such as gasoline vapour and propane; a battery, while being charged also generates a small amount of equally explosive hydrogen gas (think Hindenberg) any of these volitile gases could be ignited by a connect / disconnect spark. If you must charge on board, ensure adequate ventilation to remove all of these gases (think bilge blower) prior to connection or disconnection. Also to limit the possibility of sparking near the battery, make charger leads fast to battery terminals then plug it in at farthest reach of it's power cord. This should eliminate sparking at the battery (assuming the red is to + ,black is to - terminals).
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Quote:
Originally Posted by sailingdog View Post
Adam-

Which battery charger did you get? Is it an intelligent three-stage charger? If not, it will probably likely fry your batteries...
I'm not understanding why a regular old battery charger is going to "fry" my batteries. I've charged car batteries all the time and haven't fried anything. I've also charged the boat batteries with the same result. A battery is a battery. If you're not permanently hooking up the charger for long-term constant use I don't see the problem. I think this guy is just charging up as needed.
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Sander-

An older style battery charger will not have bulk, absorption and float stages... and as such will generally run at a higher voltage than the battery requires when it is nearly fully charged... and doing so generates excess heat and boils off electrolyte in the case of wet-cells, and just fries the gel in gel cells and AGMs.. If he leaves an old-style battery charger connected for any significant period of time... which is necessary to get the batteries up to 100%, he runs a much higher risk of frying them if it isn't a smart charger.
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Old 11-04-2008
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Quote:
Originally Posted by sander06 View Post
I'm not understanding why a regular old battery charger is going to "fry" my batteries. I've charged car batteries all the time and haven't fried anything. I've also charged the boat batteries with the same result. A battery is a battery. If you're not permanently hooking up the charger for long-term constant use I don't see the problem. I think this guy is just charging up as needed.

Basic, cheap battery chargers generally charge at only 14.4 - 14.6 volts regardless of the acceptance rate of the battery being charged.

A "smart" charger will charge at, depending upon the battery type setting, 14+ for the bulk phase, 13.8 for the absorption phase and 13.2-13.4 for the float phase thus causing no damage to the batteries.
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Old 11-04-2008
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I think most of the replys assume you will attach the charger and leave it connected for the winter. If so, they are correct. You need a smart charger that will not overcharge the batteries.

If the intent is to periodically top off the batteries by attaching the charger for a couple of hours, then I see no problem. I use this technique when my boat is on the hard for the winter.
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If you're using a "dumb" charger to top off the batteries, you should check the water level more often than if you're using a smart charger.
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Old 11-04-2008
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I got my batteries through last winter on the hard using an old automotive charger. I might have had it plugged in for 5 or 6 hours every few weeks or so. Didn't notice any more frying than they already appeared to be I only used the charger while I was there doing work or hanging with the boat, never left it running unattended.
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