Exchange old batteries with new ones when there is any abnormality in appearance or characteristics. When the batteries are connected in series, the batteries in one string should be exchanged together.
Exchange batteries for new ones before they are used for the expected years in trickle charge (or float charge) below 77°F(25°C) around them. The interval of this exchange should be shortened by temperature increase of every 50°F(10°C).
The batteries deteriorate depending on the duration time of charge and the increase of the temperature when they are used in trickle charge (or float charge). At temperatures higher than around 104°F(40°C), the life of the batteries becomes very short.