To increase the life of the battery, you please see the following points and try to follow,
1. Keep the battery terminals corrosion free and rust free. Rusting and corrosion are bad for battery performance. Rusting in terminals reduces the current flow to and from the battery. This restricted flow of current results in slow battery charging which ultimately reduces battery life and eventually effects your inverter back up. If the terminals get corroded pour hot water + baking soda solution on the corrosive area or use a toothbrush for cleaning. This will remove the corrosion. Once the terminals become corrosion free, apply petroleum jelly on to the terminals, nuts and bolts to avoid future corrosion.
2. It is important to charge the inverter batteries correctly in order to maintain the backup. After installation use battery on a regular basis. If the power cut does not occur, discharge the battery completely once every month and then recharge it.
3. Check the water level of battery every two months. See that the water level is maintained between the maximum and minimum water limit. Always top up the battery with distilled water. Do not use tap water or rain water as it contains excess minerals and impurities which affect the life and performance of the battery.
4. Change the batteries of the inverter if they are worn out. After some time the batteries lose their capacity and reducing the backup. Buy good quality batteries that will last longer and also guarantee the correct charge storage capacity. Poor quality batteries fail prematurely and do not offer sufficient backup. Maintenance free or sealed batteries are best suited as these won't leak the electrolyte. There are other types of batteries as well as lithium batteries which can be used for back up. Tubular batteries are the most efficient batteries. They have a complex design, great efficiency, longer operational life and low maintenance.