The amperage capacity is normally described in Ampere-hours. In the simplest terms, a 1 Ah battery will give you 1 ampere for one hour, over the battery's rated operating voltage. If it is fully discharged it will take 1 ampere for one hour to recharge it.
There are many other subtle characteristics. The operating voltage of a 12 volt lead-acid battery is approximately 10.5 to 14.5 volts for discharge to full charge. The Ah rating is not linear for charge or discharge, and it depends on the battery design. A car battery and a golf cart battery have very different characteristics for the same voltage and Ah ratings.
Going to a slightly larger battery as you want to do should not affect your feeder. But, the battery charger in the feeder may not have the capacity to keep the bigger battery at optimum charge, thus shortening its lifespan.
Ken
