Usually, the higher amperage output of a charger, the faster the charge time. But, unless you have a charger made for charging several batteries at a time, adding the three battery charging strip will not tell the charger that you are charging three batteries. It 'thinks' one battery is being charged, so it limits the amperage to the highest safe level for the battery. I'm assuming you are using the phantom charger.
For my current use, two charged batteries gives me all the flight time I want, at one time. Once I get home, charging one at a time is fine, for me. But, I can see situations where you might want to charge all of your batteries at the same time. Currently, the only option is going to another smart charger as the Phantom charger won't do what you want. Assuming, I understand what you want!!
p.s. To elaborate on the strip that lets you charge three batteries, the current that would normally go into one battery, is going to be divided by three. So, each battery gets a third of the amperage it would have gotten if you charged one at a time. This is assuming all batteries are discharged to the same point. So, three times the time to charge one battey. You gain nothing over charging one at a time, except for having to monitor the charging and putting in another battery.
