Do not use an automotive battery charger to charge small sealed lead acid batteries. Car battery chargers are designed to work with big SLI batteries and charge at a high amperage. For small batteries like 6V 5Ah or 12V 9Ah this will be too much amperage. Although it will charge the battery, it will significantly reduce the life time of the battery and will likely cause permanent damage to the battery.

To charge small sealed lead acid batteries, buy a sealed lead acid battery charger that charges small SLA batteries at approximately 1A. A trickle charger is perfect for sealed lead acid batteries, it a slow charger but will ensure a long life time for your battery.