It depends on what you are trying to do: keep a battery topped up and maintained, or quickly recharge a dead battery.
For maintaining: The low amp smart maintainers make a good, low-budget way to keep your battery topped up, even if there is some parasitic drain (which almost all modern vehicles have, to differing degrees). Good examples of this:
BatteryMINDer 1510, or the
Noco Genius 2 for portable units, or the
Noco 2D or
BatteryMINDer 1215C for on-board "permanently" mounted units. On Board charger maintainers typically have better water/weather-proofing and ring terminal connections to your battery. You just plug into an extension cord when needed. They
can recharge a dead battery, but will take a
long time to do so for a car or tractor sized battery.
[Note: I'm not much of a fan of the Noco Genius 1 charger, mainly because it has basically no water resistance: IP60 rating. Not an concern if you will never be using it where you get caught in a light rain, or where condensation is an issue, but I just don't trust that I will always be using it in dry conditions.]
For recharging a good sized dead battery (i.e. bigger than. motorcycle battery), you'll want a higher amperage charger, probably something in the 5-10 amp range. (There are larger chargers if you need a quicker boost to get started quickly, but these days, with the advent of small portable & effective jump boxes/boosters, they are usually the way to go for a quick start on a dead battery.) In the portable units, the
Noco Genius 5 or 10 or the
BatteryMINDer 128CEC2 are both good choices. For onboard chargers with higher amps and very good weather/waterproofing consider the
Noco Gen5X1 or the
Noco GenPRO10x1.
Personally, I don't see a point of an on-board higher amp charger like these, except in special applications. A less expensive, low amp maintainer should keep the battery topped off when not in use. If something happens and the battery does get discharged, I just temporrily connect one of my higher amp chargers. (I do have a Noco GenPRO10x1 mounted on my dump trailer. It's an electro-hydraulic dump powered by a 12 V deep cycle battery. Since it's often used in situations where the vehicle is not set up to recharge the trailer battery, it tends to get drawn down further.)
Differences between Noco and BatteryMINDer chargers:
Both are good, reputable brands. Both are temperature compensated (adjust charging voltages to optimal levels based in ambient temperatures), both are desulfating chargers, Bothare multi stage, smart chargers and can be left connected to a battery long term with out risk of overcharging and boiling off electrolyte.
All Noco chargers use high voltage pulses to desulfate. The pulses are very brief, but per email communications with Noco tech support, if you have some very sensitve electronics connected to whatever you are charging, you should probably disconnect the battery when using one of these units. (Having said that, lots of people, including me use them on modern vehicles with all of their computer controls without issue.) Noco Chargers also only desulfate in the initial portion of the charging cycle (or when you manually select "repair mode" on those chargers which offer it.)
All BatteryMINDer charger/maintainers use high frequency pulses to desulfate. Which are less of an issue for sensitive electronics. They also run the desulfation mode continuously, not jus at the beginning of the cycle. For desulfation method, the edge goes to BatteryMINDer
The low Amp Noco maintainers have selectable charging profiles for various battery types (flooded lead-acid, AGM, or Lithium). The low amp BatteryMINDER units have a generic profile to cover flooded lead acid or AGM. This is less optimal for specialty AGM (such as Oddysey AGM batteries), which generally call for a few tenths of a volt higher charging and float voltages (though some AGM batteries, such as Optima, call for the same voltage ranges as flooded lead-acid). A specialty AGM battery generally will not be damaged by charging/maintaining at slightly lower than optimal voltages, especially if the maintiner desulfates. However, it may not be charged to 100% full capacity. The edge goes to Noco on this characteristic.
[BatteryMINDer does make a specialized 2 amp AGM charger. It's more expensive than other low-amp chargers, but does include better diagnostic and display features. Still, it's a single-purpose charger.]
In the higher amp portable chargers, Both Noco and BatteryMINDer offer selectable charging profiles (flooded lead acid, specialty AGM, Lithium). Their portable units are all reated IP65, which is pretty good for weather resistance. All temperature compensate, all have desulfation, all can be left connected to a battery long-term without damage - so once a battery is charged, they act just like a battery maintainer. In my opinion, the BatteryMinder unit still has a bit of an edge in the type of desulfation (high frequency vs high voltage). The BatteryMINDer init also alows you to select the maximum amperage (2, 4 or 8 amps). On a car or tractor battery, that probably makes no difference: you'll likely just leave it on 8 amps all the time. If you want to charge a motorcycle or ATV battery, the 2 amp setting should be used (most of those smaller batteries specify a lower max charging rate). That selectable charge rate may make no difference to you if you have none of those smaller batteries or if you already own a low-amperage charger/maintainer for those batteries.
My preference is generally for BatteryMINDer, though I tend to use them interchangeably. I do use a Noco Genius 2 on my wife's motorcycle, which has an AGM battery which calls for the specialty AGM charge profile.
There are other good, reputable brands of chargers out there. I settled on these two after a lot of research. That doesn't mean some of the others aren't just as good. There are also some crappy brands/chargers out there. Quality control on some brands is highly variable: if you are lucky, you'll get one where the voltges at the various chaging stages are right where the should be. If you are unlucky, that same model sitting next to it on the shelf might overcharge your battery and boil off electrolyte.
** sorry for the length of this post. I spent WAY too much time researching chargers, and get carried away when I talk about them.
