An hour of charging may not fully charge the batteries.
Before anything have all your tools etc at the ready.
Make a solution of a few tablespoons of baking powder to about 8 oz water. Use a brush to apply and clean off the top of the batteries and connectors. Rinse well afterwards. As mentioned above clean the terminals and connections. later spray with a red antioxidant to protect the connections
A battery hydrometer from walmart will help tell you the condition of each cell. very easy to use. before you start to charge batteries use the hydrometer to record the value of Specific Gravity of each cell. If you have a low value on one cell that may be an indicator of some problem. important - before charging make sure the plates are at least covered with distilled water so as not to damage the cell barrier strips or burn the plates
I would use a good battery charger to fully charge my batteries over night at a slow or low rate so as not to overheat them. then check with the hydrometer again and note any low cell. Harbor freight has a nice unit for under $50 https://www.ebay.com/i/122900698237?chn=ps
the fully charged battery will now have a higher water level as the plates swell some. set it for regular battery and a low charge rate.
Now you can fill the cells to the slotted point of the filler. Use a flash light to inspect. I use a regular disposable water bottle with a little hole in the screw on top and stick it in the cell and squeeze a little to fill the cell to proper level. My batteries usually take about 8oz per cell every 9-10 months.
After all the cells are full, reconnect the wires and spray with anti corrosion spray you got at walmart. always cheaper than at autozone etc.
Finally, done NO now you should charge the batteries again to get the full charge. and afterward check with the hydrometer to insure all cells are at a full or near full capacity of specific gravity.
My AGM starting batteries are now 12 years old and still cranking. My 6 v house batteries are now three almost four years old and all cells are perfect.