With the constant evolution of technology in today’s modern vehicles, the days of straight forward dual battery setups
are becoming a thing of the past - Variable Voltage Alternators are now becoming standard issue in most modern
The type of equipment you may need to correctly charge and maintain your auxiliary batteries depends on whether
your vehicle has this technology or not. Variable Voltage Alternators are also commonly known as ‘Smart Alternators’
or ‘Computer Controlled Alternators’.
The natural question to ask is, how do I know whether my vehicle has a Variable Voltage Alternator?
Variable Voltage Alternators require some sort of battery sensing technology to determine load coming from the
battery and this is done by a battery sensor which is found on one of the battery terminals (usually the battery
negative). Please see pictures below for examples.
No; Because of the way Variable Voltage Alternators work, there are several situations in which the output voltage
is either too low, too high or not charging at all (hence ‘variable voltage’) therefore it's not possible to charge your
auxiliary battery correctly and to 100% state of charge. The BCDC1225D, BCDC1240D or Manager15 or Manager30 should be
used instead of the SBI12 to compensate for these situations and to charge and maintain your auxiliary batteries to
No, this is not required; All you need to install is a BCDC1225D or BCDC1240D or Manager15/30 and to charge your
auxiliary batteries effectively.