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I use a 750mA Battery Tender on my jeep because it sits for months at a time. Works great.

Anyone wanna know how long it takes a 750mA battery tender to fill a completely drained battery to full? 3 days.
 

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Discussion Starter #5 (Edited)

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The best charger depends on the charging requirements of your battery. They vary quite a bit based on battery type and the manufacturer. FWIW I ended up buying a Marinco 28106 6 amp charger for home base charging of my Concorde Lifeline AGM batteries. It's charging properties of 14.3V for bulk and absorption phase and 13.3V for the float stage match up well with the recommendations for the Lifelines.

There are many other details you can dwell on if you have the time and inclination, like the charging amperage at which the charger moves to the next charge state, the minimum optimal initial charging amperage, whether a higher finish charge voltage should be applied......... the law of diminishing returns kicks in here somewhere :)

The Marinco is $79 and only lacks temperature compensation which is very important if you need to use the charger over a wide range of temperatures. I don't need that at home, so the Marinco is a good match for my batteries at a decent price. For in the field charging I have a Ctek 12V charger and a Bogart Engineering SC2030 Solar charger that do have temperature compensation. The SC2030 is also very programmable for different battery charging profiles.
 

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I've gone through a half dozen, this is what I currently use for my Odyssey starter as it is recommended by the manufacturer:

Odyssey OBC-20A Portable Charger
 

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I have a NOCO G3500 I use on my KTM. I connected the NOCO to my Interstate wet battery in my Cherokee - it wouldn't charge it. So I used my old reliable Schauer 10A and it brought it back to life.

NOCO Genius G3500 6V/12V 3.5A UltraSafe Smart Battery Charger https://www.amazon.com/dp/B004LWVEKS/ref=cm_sw_r_cp_api_Dbd.ybRSS7QK5

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Most of the newer "smart" chargers are of the pulse charge variety, which are great for desulfation, but they have a "sense" circuit which must see 1.5 to 2.0vdc before they will turn on and start charging. If you run into a completely dead battery, sometimes there is a way to get a smart charger to work. If you have a second (charged) battery nearby, try connecting it to the dead battery in parallel and let them remain connected for a few minutes. The two batteries will begin to equalize and the dead one will accept some charge from the other battery. Once the discharged battery has enough charge voltage, you can start the smart charger and finish the charge.

A faster way is to connect the dead battery to the smart charger, then connect jumpers in parallel to the good battery, immediately turn on the smart charger and remove the jumpers. Once the smart charger can see at least the required voltage, it will remain on and charge the discharged battery.
 

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I use a Schumacher 2A/40A with 200A engine start. Comes in handy when Wifey leaves lights on and parks in middle of the driveway.
 

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There may be some really intelligent chargers out there. One thing to keep in mind is not all batteries are the same. Some batteries require different charge patterns to optimally get the best charge out of them. For instance the Odyssey battery I use recommend 14.7V during charge and 13.6V for float.

A NOCO Genius G7200 12V/24V 7.2A is smart enough to apply 14.8V for the setting 12V Cold/AGM, but other chargers may apply a lesser voltage.
 

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I would totally use that 40 year old charger on an AGM battery...
electrons have not changed much in the last 40 years, and despite being all fancy pants and stuff, AGM's are still just your good old lead acid tech at heart...
that said, you will need to manually watch it and remove the charger before it has a chance to over charge the AGM... it sure is easy to cook an AGM...
and they don't like it very much if you cook them...
 

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I don't know if this is the "best" charger, but I have been using this Schumacher charger for several years now and it works great. It works on 6v and 12v batteries. It also charges standard, AGM and gel batteries and it has a battery maintenance mode. They are $41 on Amazon.


https://www.amazon.com/Schumacher-SC-1200A-CA-SpeedCharge-Automatic-Battery/dp/B000BQSIWK
Can't reiterate enough, check with your battery's manual for what charge voltage it recommends. I looked up the manual for this charger and it does not state what voltage it uses, it just notes 12.2-12.7V "needs charging", I don't know if that means it only applies a voltage of 12.8V or what. The Odyssey charger I linked earlier costs twice as much, but it is clear in the manual:

During this mode the “Charging” indicator will be red. The charger will
use all of its available charging amps (as controlled by temperature) until the battery voltage is raised to 14.7VDC.
 

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