Do yourself a favor... read, do a search here. These are not throw away Energizer batteries. They require maintenance. They require supervision at times when completely recharging. They require that you add ONLY distilled water to each cell, and that the electrolyte level is maintained regularly.
You can use them as you have in the past, and replace them regularly, or you can show some care, by maintaining them, and having their life extended considerably.
You need a charger that will get the combined two batteries showing 14.8v at the battery terminal posts to fully charge your batteries.
You should strive to store your batteries and put them away with a resting voltage of about 12.73 Volts at 72F.
Search, read, using terms like "Bulk charging" "Absorption Charging" and "Equalization charging".
Pay attention to the voltages needed to bulk charge, absorption charge and equalize charge, because they need to be provided by your charge controller, and most likely to equalize charge, by a battery charger at home, hooked up to the electrical grid, not your generator.