A secure supply of energy is the foundation for the success and continuity of many enterprises be they industrial plants, offices, healthcare facilities, utilities or data centers. For some of these concerns, power outages can be very expensive indeed, with costs sometimes running into the tens of millions of euros. This is why many businesses install an uninterruptible power supply (UPS). A critical part of the UPS is the battery bank that provides the energy needed to ensure that a continuous flow of clean power is available to the critical process that the UPS is powering. Parameters that have to be taken into consideration in properly selecting battery systems are the desired power and autonomy, inverter efficiency, final discharge, and available charging voltage. These and many other factors must be carefully considered when selecting and configuring UPSs and batteries. When dimensioning the uninterruptible power supply system, a comparison of VRLA and lithium-ion batteries was made and their advantages and disadvantages were described. When dimensioning and designing the data center itself, many factors and parameters need to be taken into account. From the exact location of the data center in terms of latitude, which affects the operation and life of batteries that are sensitive to extreme temperatures, to requires of the customer and the type of load to be protected. From this information we can get an initial vision of the requirements and specifications that the required UPS needs to meet. The choice of UPS is based on the information about the stability in the network to which it is included and the required degree of critical load protection. Independently, they can be used in two UPSs in parallel mode. There are three basic UPS topologies. Dual conversion UPS, line-interactive UPS and passive UPS. UPS dual conversion is the most reliable, ie it offers the most secure protection to critical load. A very important part of the UPS is its battery system, which consists of a battery cabinet, batteries and monitoring and protection system, and each of these parts of the UPS must be carefully designed and dimensioned to avoid unnecessary construction costs, and ultimately the main reason for using the UPS, power losses and power irregularities.