Older panels sometimes get replaced when the (usually 20 year) warranty wears out. Often by then the panels are putting out somewhat less than their rating. Most warranties say something like "guaranteed to produce at least 80% of rated power for the life of the warranty".
So if they work (they probably do), they might put out a bit less than they did when new.
Another reason they get replaced is because newer panels produce more watts per square foot, so if the warranty is expired anyway, and the cost has been amortized, what the hell, buy some new ones and get more power on the same size roof.
Those are "24 volt nominal" panels. The open circuit voltage (in sun, no load) is 43v, but the "rated voltage" (that's the same as Vmp - voltage max power (under load)) is 34v. 34v is high enough to fully charge a 24v battery bank, but not high enough to fully charge a 36v battery bank. Hence, "24v nominal".
To charge a "12v nominal" battery or bank, you will need an MPPT charge controller to step the voltage down from 34v (if panels in parallel) or 68v (if panels in series) to the 10v-15v range needed to charge a "12v nominal" battery.