Which Side Do You Connect First On A Battery. It should also be the last cable to remove when complete. Technically you may not need to disconnect the panels before disconnecting the battery.
So connecting the lead first is safer. Once you disconnect the battery you can proceed to clean the entire area getting everything ready for your replacement battery. Next lower the battery onto the battery tray with the terminals in the right position and clamp it into place.
Now connect the new battery in the reverse order connecting the positive terminal first then the negative.
Any mistake with the other lead will lead to a short. Disconnect the jumper cables in reverse order. Before the wiring you first remove the cover and loosen the connection lock and then your will see the wiring terminals for solar panel battery load as well as temperature sensor and Rs 485 port for PC. Or replace the batteries at night.
