How long will a deep cycle battery last?

How long a battery will last in terms of its usable life depends entirely on the following:

• how often the battery is discharged and charged
• how fast or at what rate it is discharged and charged
• to what depth it is discharged (DOD) each time
• how well or properly it is recharged after each discharge, and,
• is it the right battery technology for the job it is being asked to do

When designing your system, the battery (battery bank) must be appropriately sized, given the job it will be required to do. Sizing that assumes a maximum of 50% DOD is preferable. Make sure that the system has proper low-voltage protection against over-discharge and that the charge source is capable of adequately charging the battery. A battery used regularly in deep discharge service should be matched with a charge source that can charge the battery in ideally no more than 10 hours giving the battery time to rest before being put back into service.

YES, and before anyone starts to complain, we are aware that many OEM equipment producers do not provide chargers that can charge the battery banks in 10 hours. No matter the battery's design life or what type of warranty is provided with the battery by the manufacturer, a battery is only capable of providing “X” amount of total capacity (i.e. 100AH battery x 150 cycles = 15000 AH total capacity). If the battery bank is undersized for the job it is being asked to do, it will fail sooner than the system design life you wanted to have. There is no substitute for proper system sizing.

This is the typical warranty and small print provided by some of the world’s premier manufacturers, and you can see loud and clear that a 4-year warranty means nothing if the battery is cycled out before the four years is up:

XXXXXXXX Products Inc. (“Manufacturer”) warrants its XXXXXXX batteries (hereafter referred to as “Battery”) to be free of defects in material and workmanship for the following Applicable Warranty Periods:

• Two years for Auxiliary Power Unit (APU) and other non-engine start cycling applications
• Two years for power sports applications
• Three years for commercial, industrial, marine and automotive applications in non-BCI sizes.
• Four years for an engine starting application for XXXX, XXXX, and all BCI sizes

The warranty does not cover a Battery reaching its expected end of life, which may occur before the warranty periods stated above. Depending on the application, a Battery can reach its expected end of life before the end of the warranty period. A Battery can deliver only a fixed number of usable amp-hours over its lifetime and is considered to have reached its expected end of life if the application uses up all of these amp-hours, regardless of the time the Battery has been in service. Therefore, the Manufacturer reserves the right to deny a warranty claim if it determines the Battery to be at its expected end of life, even if the claim is lodged within the applicable warranty period.