We have three back up power supplies in the house. As you probably know, the batteries don't last forever. Well, two of our back ups need new batteries. So you go to the manufacturer's web site to order a new battery. You notice right away that they are very expensive, about $45-$50. So I started searching around and discovered that there are many batteries available, the difference being the terminals and the amp-hour rating. They are all SLA (sealed lead acid.) Finally, I found a suitable replacement at half the price. We will see how it goes when I get them installed.