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Battery Charging Question

Old 03-20-2007, 07:02 PM
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Default Battery Charging Question

For simplicity sake let's just say there is only two different ways to charge a battery, one is by the engine while it is running and the other is on the work bench via a charger.

Ok let’s say the alternator on the boat is only capable of 35 amps a WOT and you run the boat @ WOT for 3hours.

Now my question is: why when you charge a battery on a charger at say 10 amps for an hour does one need to loosen the battery caps to charge the battery? One doesn’t loosen the caps while the battery is being charged on the boat at 35 amps. ??? Now if we are talking about a car/ truck you could very well be pumping out 75-100 amps, yet one doesn’t loosen the battery caps. ??? Why do we loosen the battery caps when we charge the battery via a remote charger? ;?
Old 03-20-2007, 07:31 PM
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Default Re: Battery Charging Question

My guess would be in case you overcharge your battery on the bench by not checking the voltage prior to full charge. I use a battery maintainer that you leave hooked up while not in use so it cannot overcharge. I dont even own a single battery with filling plugs, they are all sealed.
Old 03-20-2007, 07:55 PM
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Default Re: Battery Charging Question

Good guess. The typical alternator on a motor has a regulator, also to prevent overcharging. Overcharging is also known as gassing.
Old 03-22-2007, 09:38 AM
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Default Re: Battery Charging Question

Voltage is what gasses a battery, not the amount of current. It sounds like your bench charger is a cheaper automotive type and is poorly regulated. I've had great performance and luck with the WallMart ones that sell for about $70 to 80. They are the ones with the digital voltage read-out. They are modern computer controlled multi-stage chargers.
Old 03-22-2007, 01:26 PM
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Default Re: Battery Charging Question

yandina - 3/22/2007 9:38 AM

Voltage is what gasses a battery, not the amount of current. It sounds like your bench charger is a cheaper automotive type and is poorly regulated. I've had great performance and luck with the WallMart ones that sell for about $70 to 80. They are the ones with the digital voltage read-out. They are modern computer controlled multi-stage chargers.
Gotta agree here. A typical engine alternator has a lot better voltage regulation than a cheap battery charger. Since the battery mfg doesn't know what you'll use, they recommend loosening the caps to better facilitate the outgassing - which really shouldn't be happening much at all if the charge current is properly regulated.

Ken

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