Monitors for Deep Cycle Batteries

There are few alternative solutions for monitoring deep cycle batteries.  Discussed below are the two major traditional methods of deep cycle battery monitoring, and the Argus LPR method.

Battery Volt Meters
Coulomb Counting
Argus LPR

Battery Volt Meters

Many cars and electric vehicles already include some type of battery volt meter, and many battery volt meters are available for aftermarket installation for use in boats, RVs and other vehicles. Typical voltmeter displays consist of an analog needle ranging from 10 to 14 volts, or a series of LED or LCD segments that turn on or off as the battery voltage changes.

While volt meters are normally inexpensive, they do not provide very useful information because volt meters are simply measures of voltage, and voltage alone is not correlated useful battery capability attributes.  .

No indication of stored energy level
A voltmeter can't distinguish between a 100Ah battery charged to 12.5V and a 10Ah battery charged to 12.5 volts.  While the actual stored energy is different by a factor of 10, the stored energy in the battery is not reflected in the voltage measurement.  Therefore, a voltmeter can't be used to understand how much energy is really available.   

Poor 'Fuel Gauge' / State of Charge information
Even if the actual energy level in a battery isn't important, a voltage gauge has very limited ability to display relative state of charge (empty to full.)  The reason is battery voltage reflects relative battery charge level only when the battery is completely at rest (not being charged or discharged).  And even at rest, measured voltage can be missleading due to surface charge effects. 

Not surprisingly it is most important to know the battery state of charge while the battery is being used. Ufortunately that is precisely when the information from the voltmeter reflects the charger or load on the battery and not the battery charge level.  The end result is that a voltmeter inevitably delivers inaccurate and premature indications of an empty battery during discharge and inaccurate apparent full indications as soon as the battery begins to rechage.

No Battery Life / State of Health information
There is no ability for a volt meter based monitor to provide any indication of battery health because battery voltage is not at all related to battery health.  Without battery health information you have no idea what condition your batteries are in. You will not know if they are up to the task or if they have reached end of life and should be replaced.

Coulomb Counting

Current counters or Coulomb-counting systems estimate available energy in a battery by carefully tracking current flow in and out of the battery over time.  Aftermarket coulomb counting battery monitors are relatively expensive, (often more than $300 per sensor) and involve two main components.  A large current sensing shunt or coil is installed at the negative battery terminal, and a separate display indicates current flow and available energy.  Besides being expensive and bulky, coulomb counters have significant shortcomings as charge level meters, and do not provide any battery health information.

Poor 'Fuel Gauge' / State of Charge information
Coulomb-counting avoids some of the deficiencies of the volt meter method as an indicator of battery charge level (state of charge) however, important shortcomings remain. Complex algorithms are required to compensate for un-measurable characteristics of the battery. Furthermore, the compensation is highly specific to the type and size of battery, limiting the flexibility of the system to be adapted to replacement batteries. Shallow discharges (common in most applications) lead to incorrect assumptions about total capacity, and total capacity values are updated only when a full recharge follows a full discharge, a rare situation. Errors often accumulate to the point where a battery may be indicated as empty, but is nearly full.  Frequent 'calibration' is required to 'clear' the system of accumulated errors associated with charge/discharge inefficiencies internal to the battery. 

No Battery Life / State of Health information
Like volt meters, coulomb counters offer no information about battery life or state of health. Without battery life information it is not possible to understand the condition of any batteries.  You will not know if they are up to the task or if they have reached end of life and should be replaced. Even more troublesome is the fact that coulomb counting monitors are not able to adjust for the lost capacity of a battery over time.  Therefore, even before considering accumulated errors, a battery that has decayed beyond end of life could be indicated as completely full and capable of providing full new capacity.   If you rely on your batteries for mission critical support for example RV and Marine applications, battery health information is of primary importance.

Argus LPR

The Large Pulse Resistance technique of the BB-DCM series coupled with a powerful microprecessor overcomes the deficiencies of the voltage and coulomb counting methods and delivers state of charge and state of health information with unparalleled accuracy and consistency. 

Accurate State of Charge detection 
By actively measuring DC internal resistance every 60 seconds, the DCM continuosly and directly tracks available energy in the battery providing actual state of charge, , and absolute capacity information at all times, most importantly, while the battery is in use. 

Automatic State of Health measurements
Because LPR tracks the growth of internal resistance, the BB-DCM is continuosly and automatically self calibrating state of health for age and temperature including the effects of sulfation, dehydration, corrosion and other battery decay factors.

Unlike the traditional monitoring techniques of voltage tracking and coulomb counting, the BB-DCM using LPR accurately answers the following important questions in real time:

• How full is the battery?
• How much energy is available now?
• How much energy could the battery hold now if fully charged?
• How much storage capability has been lost since the battery was new?
• How much battery life remains?
• When to recharge the battery?
• When to replace the battery?

Learn more about Argus LPR for battery monitoring.

* Only accurate when not using batteries
** Only accurate for new batteries and recent calibration
*** Some models and / or some conditions only