Note: Requires either a 100 amp or 500 amp shunt. An "RV" version (TM-2025-RV) is also available - major difference is color, same price. It comes in two versions which are identical except for physical size and label color. - TM-2025RV version is a little less wide than the TM-2020, comes with its own cream colored enclosure designed to be surface mounted to a wall, so does not need an additional mounting enclosure. The label colors are more subdued than the TM-2020: beige and black. - TM-2025A is physically virtually the same as the TM-2020: it mounts in a double gang electrical box,and is not furnished with an enclosure. The label colors are silver text on dark blue with orange border, identical to the TM-2020. The TM 2025 is intended to help maintain battery systems for 12V to 48V deep cycle battery systems, such as ones found in RVs or off grid homes which are regularly charged and discharged. The amps or watts display measures the rate of energy going in or out of your batteries so you can check your charging systems, and also to see how much energy each of your appliances use to help you conserve energy. The % Full display will help you keep track of how charged or discharged your batteries are. The volts display will let you discover if your charging systems are charging to the proper voltage, which is important for maximizing your battery life. The days since charged display shows how recently the main battery (system) was fully charged, so if it hasn't been charged recently you can perform extra charging if necessary to help maintain the capacity of your batteries. The TM-2025 also can measure the voltage only of a second battery set, such as the starting battery, or solar voltage input to a charge controller.