Not all Black Boxes are the Same; Proper Charging & Depth of Discharge

Written By: Randy Anderson - Technical Sales & Training Manager

Proper charging and Depth of Discharge (DOD) are two critical factors that will affect the life and number of cycles an AGM Traction plate battery can deliver.

We recently visited the site of a large pharmaceutical manufacturer who utilizes Discover AGM traction batteries in their floor scrubber equipment.  Several weeks prior to our visit they had returned a set of batteries that showed signs of misuse.  When we arrived on site, the first thing we checked was that the charger (Delta Q 912-2400) was programmed with the proper charging algorithm, Alg 43, and it was.

Next we checked the voltage on the two batteries connected in a 24-volt configuration. The batteries measured 12.06 & 12.09 volts each. This would indicate that the batteries were at approximately 25% SOC (State of Charge).  A log report on the machine indicated that it had last been used the prior evening for about 20 minutes, so one would expect to see a much higher SOC.  After reviewing the machine usage log for the prior week and speaking with the Supervisor of Cleaning, we discovered that the batteries were only being recharged when they reached a level of 20% SOC.

All manufacturers of deep cycle and traction batteries, whether they are flooded, AGM or gel, state that the number of cycles a battery will deliver depends on DOD. This number varies by manufacturer and type of battery from 300-500 cycles at 80% DOD to 2000-2800 cycles at 20%. For this reason, it is only logical that deep discharging batteries to 80% DOD or greater should be avoided whenever possible as reducing the depth of discharge will greatly increase cycle life by as much as 4-6x depending on type and manufacturer.

Many people are under the impression that the lead acid battery has a fixed number of cycles that it will deliver over its life regardless of depth of discharge. For this reason, they will often discharge the battery to extreme low levels with the intention of getting the most out of their battery pack when in fact they are reducing the life and number of cycles the battery will deliver.

If in doubt about how to maintain your batteries or what type of service will get the maximum useful life out of a battery or battery pack, consult the manufacturer.  It is important to note however that although each manufacturer may have a slightly different recommendation on operation and maintenance of their battery, deep discharging of lead acid batteries should be avoided or minimized in order to optimize overall life and capacity.

If you have any other questions about this topic or any others, please contact us!

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