We generally recommend that customers who buy Hydropump DH900, DH1800, and PH3000 battery backup sump pumps use a Marine Sealed Lead Acid battery, in size 27. Since it is sealed, this type of battery is maintenance-free and does not require its fluid to be topped off periodically.
Other battery types can be used with Hydropump pumps as well, including AGM (absorbed glass mat) and Gel type batteries. Since each battery's characteristics will be slightly different, you should check with the manufacturer to find out the battery's life expectancy and requirements before purchasing.
Also, make sure the battery manufacturer's warranty covers you for at least 1 year. Automotive stores typically carry a wide variety of batteries, and their staff should be able to help you pick from the available battery types.
This article is intended for informational purposes. Before beginning any construction project at your home, please ensure that you take necessary safety precautions and consult construction professionals whenever necessary.