What's the best method of charging a car battery?

I have a 12v car battery (not using in a car) and I also have a fancy charger (I use this to charge batteries for RC vehicles) that can alter voltage, current, end voltage and so on.

What voltage and current should I charge at, and what should the voltage be when it's fully charged (so I know when to stop)? (the charger suggests 14.7v)



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A power supply that regulates voltage to between 13.8 and 14.4 volts, and limits charging current to C/5 or less is a good rule of thumb.  C being the battery capacity in ampere-hours, so with a small 10 A-H gelcell, you'd limit the charging current to 2 amps or less.

12V Power Wheels "Quick Chargers" can be used to charge car batteries.  They put out several amps in "quick charge" mode, then 1A until the battery is 100% charged, then switch to a pulsed trickle charge mode.  I picked up a couple at a thrift store; they're small enough to keep in the car or in a drawer of a tool cabinet.  I cut off the alien Power Wheels connector and added a couple of battery clips.  A few amps may not seem like much, but on a couple of occasions where lights were left on all day or overnight, it only took about a half hour charge to revive the battery enough to start the engine.
lemonie7 years ago
Car batteries are pretty tough, you can put 2-4 amps through them, and the more you do the quicker they charge. But you need more than the 12V to do it (seandogue).
You can judge full charge by how much current it's taking, if you wire an ammeter in there. Or have an idea of the capacity and how much it's been used.

true that. in fact, a lead acid battery charger for charging automobile batteries will often put out as much as ~16-17V in fast charge mode in order to boost the charging current to a reasonable level to get it up and working quickly. (not the best method for longevity, but acceptable if only done once and a while) ...speaking for regular auto batteries that is....deep discharge are more forgiving.

(why the citation? fwiw, if "13-14V" was criterion, I meant what they will read when fully charged, not the charging voltage))
Re-design7 years ago
Put it in a car get the car started and drive from LA to NYcity.  It should be well charged by then.
JimFlo7 years ago

you can usually get the battery data, including charge rates, voltage, amps, and temps from the manufacturer or their web site. Every battery is slightly different.

seandogue7 years ago
full charge at ~13-14V. A simple RC battery charger is probably not going to supply sufficient charge current for a car battery with any appreciable discharge, although it might be okay for a float charge.

Best option for an uninstalled car battery is a car battery charger.
you need to be careful about not applying too much voltage across an automobile battery, or in fact any liquid cell battery pack, because hydrogen production accelerates at higher cell voltages, increasing the possibility (real) of an explosion.
kirdaiht7 years ago
charge at a voltage a bit higher then 12. (try 13 - 14) As much current as possible (more current = faster charging) and have it stop when the car battery reaches a voltage slightly higher then 12.