Batteries in backup applications
Batteries in backup applications are maintained fully charged, usually in floating condition waiting for some power outage, to undertake the supply of the loads.
During this floating condition the battery is allowed to drain a small trickle current that will keep it fully charged, compensating for its self discharge and leakage requirements.
This current is almost equal to the average of the requirements of all the series-connected individual cells (or blocks) of the entire battery. The requirements of new, same-make cells are initially quite similar, but will soon begin to differentiate due to uneven temperature distribution, manufacturing tolerances, ageing etc. of the individual cells (or cell blocks). The differentiation accelerates regeneratively until some cells, that require more current, will gradually be driven to starve, undercharge and finally to sulphation, while the others that require less current, will be driven to overcharge, corrosion, overheat, dry-out and sometimes to thermal run-away.
This procedure is usually quiet, and will only be detected during the next power outage, when the battery will fail to behave as expected.
The duration of this course in most cases is, by some … strange coincidence, a little more than the warranty period of the batteries, (about 5 years), while their service life specification is much longer, usually 12-20 years!
Our Active Battery Management systems, for backup applications, control the trickle current individually for every cell (or cell block), according to its own detected specific needs. This eliminates the unnecessary stresses and allows the battery life to extend beyond the manufacturers service life specifications, almost up to the shelf storage life limit.
While the battery is set in floating condition, the cells are actually disconnected from the charger, remaining of course continuously ready to undertake backup action, through steering diodes. Each one cell is periodically tested for OCV and internal resistance and trickle current is applied when necessary by its dedicated charger.
This mode of operation covers usually the 95-99% of the battery life, between power outages and is exactly equivalent to shelf storage in ideal fully charged conditions, without any stress at all. This is the reason for the remarkable improvement in service life.
Lossless full discharge test is supported, for ultimate battery test and capacity measurement.