good day,
connecting solar panels in series is generally a good design choice.
each battery charger has a maximum safe voltage input limit. some are 75 volts, some lower, some much higher. it's very important to set it up so that voltage limit is never reached in practice.
temperature will change the voltage of a solar panel. usually colder means higher voltage. often listed as a percent change per degree C. usually 25C is the base temperature.
connect two identical panels in series, that will multiply voltage by two.
the safest way is to find weather record of lowest temperature ever seen in the location(s) it will be installed at, then calculate what each individual panel's voltage would be at that temperature, then use that to calculate how many can be connected in series before magical smoke might start escaping from the charger.
this way, if you have three "40V" panels connected in series and expect 120V max and connect it to a charger than can only handle 130V max, the low temperature at your location can cue you into limiting to two in series if it results in more than 43.33 V sort of deal.
hope this helps, good luck with your project