How to use a float or trickle charger

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a maintainer device- like a battery tender brand used on boat 12 v batteries.. I have a car that is not driven but a few times a month. can I hook up the float charger without disconnecting one battery cable? that is ,if the car is off, and I hook up the float charger, and leave the car off, will it harm any part of the electrical system?
 
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No,removing a cable isn't necessary. But, if the battery is in good shape, taking a cable off would be all you need to do for a few months.
 
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Connect the thing to the battery properly and plug it in. I've got a cheapo HF float charger I use for my old BMW over the winter. Some here predicted dire results for the batt, but after three winters of storage using this five dollar device, the battery seems perfectly happy.
 
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Originally Posted By: fdcg27
Connect the thing to the battery properly and plug it in. I've got a cheapo HF float charger I use for my old BMW over the winter. Some here predicted dire results for the batt, but after three winters of storage using this five dollar device, the battery seems perfectly happy.
i have 2 and both cooked my batteries.
 

JHZR2

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Originally Posted By: fdcg27
Connect the thing to the battery properly and plug it in. I've got a cheapo HF float charger I use for my old BMW over the winter. Some here predicted dire results for the batt, but after three winters of storage using this five dollar device, the battery seems perfectly happy.
Nobody predicted dire results, but three winters is hardly impressive, and it is well known in the industry and by the manufacturers that thermal compensation is best practice for longevity. OP, lead acid batteries last longest when maintained at full state of charge. They do self-discharge, but that is slow and temperature dependent. Removing the battery cable will prevent parasitic discharge via the vehicle, which will slow down overall depletion to just self discharge. Putting it on by maintainer will prevent any discharge keeping it healthiest. A temperature compensated maintainer is best. Practically speaking for the sitting duration you have, unless you're seeing issues, you may not need anything (assuming you charge fully each time you do use it), and depending upon your change-out interval, may or may not have a benefit. I keep our batteries 10+ years since they are maintained and tested, so the economics of buying a maintainer was easy.
 
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I've had my Neon being maintained for a few years with a Battery Tender Jr. The car may sit for a couple weeks or a couple months. Starts every time. Very simple hook up, I have the semi-permanent o-rings on the battery terminals so I just have to plug the tender into that and plug the tender into the extension cord and hide it under the hood, away from the battery. It also comes with clamps for more portability between batteries. Then just unplug from the extension, unplug from the pig tail and off I go. It's all outlined in the directions.
 
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Those little power supplies you plug into the wall and they power your cordless phone or modem or whatever. If they say the output is 12-18 volts DC. I save them [when throwing out the device] and put alligator clips on the ends. They work as a trickle charger and they are free. Don't seem to last though. Quit for no reason sometimes. Try it for a few hours and make sure they don't get to hot. Usually put out about 0.1 amps.
 

JHZR2

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The load impedance is too low for those wall warts, and the current limit doesn't seem to work right. The battery charger units properly impedance match so they can last for years.
 
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I have a battery tender with a cigarette lighter plug on the end. I'll just run the cord through the window and plug it into the cigarette lighter and it charges the battery. It won't work if your cigarette lighter only works when the car is on, but for both of our cars (and bikes, which we've added cigarette lighter style power outlets to), it works perfectly. No opening the hood, removing the seat, disconnecting any cables, or anything like that. My wife has a habit of leaving her lights on and completely draining her battery, even after she's had to pay for two new ones.
 
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The most basic trickle chargers can cook a battery if left on continuously. A household timer set to turn on 1-2 hours per day solves the issue.
 
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Originally Posted By: Anduril
I have a battery tender with a cigarette lighter plug on the end. I'll just run the cord through the window and plug it into the cigarette lighter and it charges the battery. It won't work if your cigarette lighter only works when the car is on, but for both of our cars (and bikes, which we've added cigarette lighter style power outlets to), it works perfectly. No opening the hood, removing the seat, disconnecting any cables, or anything like that. My wife has a habit of leaving her lights on and completely draining her battery, even after she's had to pay for two new ones.
You could try and set it up the way that a lot of boat owners hook up a maintainer. Some will just more or less permanently mount the maintainer somewhere, and then bring in an extension cord. Or get a standard cable and connect it to the posts. A lot of maintainers have a standard connector and you can secure it and have the connector hanging out the bottom like a block heater connector. This one is meant for small batteries, but it should be possible to splice one of these into secondary battery cables.
 
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