A picture is worth a thousands words. In this case, 290.
Canadian Tire, 1/2 price for $30 + tax (12% sales tax here. Yes folks, that is correct....12%), so I got six of them. I brought my multimeter to the store to make sure they are isolated, checking for continuity between the input and output side: OL. At home I hooked two chargers up to a couple of batteries and checked for voltage differences between the positive of one battery and negative of the other battery, negative and positive, positive to positive and negative to negative (overkill just to make sure): OL. Then I just took a wire and did the same, looking for a spark: nope. All good news.
My reason for choosing individual chargers isn't because of cost, although these were pretty cheap (and I do have another Schumacher one coming from Amazon as well). I could have bought a used 72V or 84V charger for pretty cheap, after all. The reason is because I have a wildly mismatched selection of batteries (older floodies, newer floodies, AGM's, etc.), and charging them in series without doing damage would be very challenging, if possible at all.
So the chargers. 10/2A. Auto shut off. El-cheapo Chinese made. Some watching with my voltmeter shows that on "automatic conventional & low maintenance" mode, they charge until 15.0V and then shut off with a continuing trickle charge. When the voltage falls below about 12.9V they turn back on. On the "maintenance-free & deep-cycle" mode, shutoff is 15.4V and turn on is 13.0V. Now to choose which mode to use. I think the lower voltage one for the "dual-purpose" floodies and the higher voltage for the AGMs. Can a battery know-it-all please chime in here?