There are plenty of different battery chargers out there, so how do you know if the one you are about to buy is the one you need?
The first thing you need to know is what kind of battery you have. Is it Maintenance Free, Wet Cell (flooded), AGM (absorbed glass mat), Gel Cell or VRLA (valve regulated lead acid). A good number of chargers will work for all of them except Gel Cell. However, there are also some Gel Cell chargers that can work with other types as well.
Gel Cell batteries are ones with a silica type gel that the electrolyte is suspended in. It it commonly mistaken for AGM, because both of those battery types have liquid in them and can ensure that none of that liquid leaks if the battery breaks.
The type of battery is not all you have to know. How many Amp hours does it store? In order to make sure that your battery does not take 11 hours to charge because the charger is not ideal, take the amp hour rating of the battery divided by the amps, and add 10% for what it would take to top off the battery. For example, a 10 amp charger would take about 11 hours to do a full charge on a battery that has 100 amp hours, or 6 hours to do a full charge on a battery with 50 amp hours.
Now that you know all of that, think about what you are actually using the charger for. Is it to keep your car or motorcycle from losing its charge if you don’t ride it for a few months? If that’s the case, a low current charger will work just fine. But if you need something to charge quickly for more immediate use, a faster charger is better for your purposes. If you have an RV, maybe you will want a charger that doubles as a power supply. Or if the charger will be outdoors a lot, such as if you need it while camping or traveling, a waterproof charger may be better than a standard one. And if you need to charge several batteries at once, there are chargers that do that, too.
Overall, if you know what type of battery you want a charger for, you have the most important part covered, because that makes it easier to determine whether or not the charger will work. After that, it depends on how fast you want the battery to charge for your purposes.