A World First! 
GENEREX BACS is the first battery management system for stationary batteries to provide a capacity display of the batteries/cell

BACS has been the key technology for active management of stationary batteries for more than 18 years. Balancing ensures the stability of lead-acid batteries and NiCd or lithium (LTO/LiFePo) based cells and maintains the "health" of the cells - SOH (State-of-Health) - at the highest level, so long as measured values / alarms are monitored correctly.

The interpretation of the measured values of a battery system is also massively improved by "balancing": Balancing keeps all cells/batteries closely within the "healthy" voltage window and thus allows for a highly precise impedance measurement, and - due to the exactly equal voltage values of all batteries during the measurement – it also enables a comparative relationship between the measured impedance values.

This has led to BACS verifiably improving both the reliability and longevity of almost any battery-based UPS concept. This makes BACS a game changer in the industry, and the first choice of most datacenter operators in the western world!
In addition to facilitating the achievement of a fully charged state and improved impedance readings through balancing, these improvements in battery capacity (SOC - State-of-Charge) can now also be measured.

Any user who has ever made a comparison of 2 identical battery systems with/without BACS is able to confirm: the effective battery capacity is significantly higher with Balancing than with an identical battery system without BACS!
Not only countless BACS users have noticed this effect, but also independent institutions and universities have been able to prove that a BACS system delivers significantly more battery capacity over time than an identical battery system without BACS. 

We have been researching this effect for years and have observed capacity increases of up to 20% in the measurement data. From these findings, we have identified a new approach that many battery system users have been waiting for:

With the introduction of firmware 2.04, a BACS system provides a percentage capacity indication for each battery/cell!

The capacity display determined by BACS is comparable to the results of much more elaborate measuring methods such as "Current Balance". With the "Current Balance" method used so far, current sensors were used to record which currents were drawn and how much was recharged during charging, but losses, temperature effects and missing information about the individual batteries/cells lead to inaccuracies. As a result, after a few discharge cycles all current balance calculations become increasingly inaccurate and the user must be aware and involved to decide when exactly a battery bank with all batteries is considered "full" and “healthy”. However, the fully charged state can hardly be determined without the provision of BACS’ Balancing, and is thus a considerable source of error in the current balance calculation. To date, the measurement of a battery capacity - regardless of the type of chemistry - is prone to error and is more of an "estimate" that could be more or less accurate, but hardly depended upon.

With the new BACS current sensors on each battery string and active balancing, BACS is able to calculate the percentage of available residual battery capacity at discharge for each individual battery/cell.

Today, we find battery management systems with lithium batteries in the automotive sector that achieve quite good capacity estimates - but at high costs, which make them less than economically viable for every application; especially for stationary battery systems this technology is hardly suitable. A UPS is not a TESLA car and a discharge in a UPS is the exception rather than the rule - this makes the determination of the battery capacity in stationary systems difficult because the state-of-health - the undetected failure of a battery/cell - can have a major influence in the calculation, and this cannot be verified due to the lack of discharge options. In a UPS, all batteries must always be considered "full" and "healthy", otherwise any calculation of a capacity will run into difficulties.
To date, the UPS display of the "autonomy time" or "battery capacity" is a curve provided by the battery service technician based on battery parameters - which has little to do with the SOC of the batteries in reality if the measured values of the individual batteries are not included. The failure of a battery cannot be detected and therefore cannot be taken into account. It is precisely this circumstance which explains why some UPS users complain that the display of the UPS still shows e.g. 80% when it is discharged, but the UPS switches off because of an undercharge a short time later.

Most UPS users have not noticed this deficiency because discharge simply occurs too infrequently to detect differences. This is true for most users - but not for highly critical datacenters or military installations. Here, the problem of poor UPS capacity indication has been known for a long time, and has led to these users performing regular capacity tests to determine the actual autonomy time/battery capacity and to recheck it regularly.

In fact, it was precisely through the provision of such regular tests that it has been repeatedly found that the battery capacity improved considerably as soon as BACS was installed. For example, an experienced large user of BACS in the USA reported that after switching to BACS, the number of batteries that needed to be replaced each year was dramatically reduced – and this coincided with an increased capacity!

With balancing, BACS not only can measure the impedance values of a battery more accurately and thus make them ultimately comparable, but, for the first time, Balancing also allows for a significantly improved capacity measurement.

But there are other advantages to visually displaying the battery capacity: 

Charging mode: The image to the right shows the capacity display during heavy charging - you can see that Balancing is 100% active and the capacity cannot currently be calculated. The capacity display shows by an arrow pointing upwards that more current is flowing through the bypass than it can dissipate and that Balancing currently has hardly any effect. Only when the battery builds up a resistance because it is approaching the fully charged state will Balancing go below 100% and the capacity calculation can be started.

Trickle charge mode: It may not be clear to every user that voltage behavior during a discharge can differ greatly depending on the battery chemistry. Many users are not aware that a nominal voltage of a lead battery of 12.50 volts - depending on the load - can already represent a massively discharged battery, and that the nominal voltage of a NiCd battery of 1.20 volts says little about the capacity - although both are the nominal voltages of the battery/cell - but with different chemistry.

However, if the capacity is displayed with a color or a measured value, even the less experienced user will notice that battery No. 4 with 11.41 volts is a problem because the capacity is displayed in YELLOW, indicating a low level. This enables early detection of defective batteries in the system in real-time without additional components and maintenance work!

Discharge mode: Also in case of a discharge, the user will be able to see which cell/block loses capacity faster than others, and check these batteries accordingly later.

In the picture on the right you can see that there is a difference of 5% in the capacity of battery no. 1 as compared to no. 2, although both have the same voltage.

This development is to be observed in order to identify whether the difference increases during discharge.

A little later, battery no. 1 still shows a 3% difference to no. 2, although the voltage at battery no. 1 is now higher than at battery no. 2 => battery no. 1 should be observed.

The optical display of the capacity makes it easier for the user to keep track of a large number of batteries and clearly indicates the vital differences between the batteries at an early stage.

With BACS, GENEREX is proud to have the first BMS on the market that can, through Balancing, provide

• Extended service life
• Increase capacity
• Comparability of impedance measurements
• Replacement of old cells/batteries with new cells/batteries without damaging the remaining ones within the string.
• Delay/prevention of spontaneous combustion due to overcharging
• **NEW** - a battery capacity indicator

Now balancing forms the basis for calculating the battery capacity – more dependably and cheaper than was previously possible!

No Battery Monitoring System can do this; only a Battery Management System can, by treating each cell or block individually, establish a common voltage base that allows the capacity to be calculated much more accurately than would be possible without balancing.

At GENEREX, we work hard to live up to our reputation as an industry leader and are proud to have been recognized as the unofficial standard within the industry by many users around the world.

The next generation of our BACS system will support new technology approaches, in addition to well-known standard technologies, and will be able to almost guarantee operational reliability for systems based on lithium LTO/LTE/LiFePo batteries. And this 4th generation will be compatible with the current most successful generation of a BMS on the market!