Dual Battery Systems Explained

Dual Battery System Types

DC to DC Chargers - Ctek D250s, Thunder DC to DC, Redarc BCDC etc.



Indepndant Charge Systems - Rotronics 2 and 3 stage systems (No longer in production)



Solenoid & Parrallel Systems - Redarc Smart Solenoid, Rotronics MH10, Piranha Dual Battery Systems etc.


Battery Types Explained

Deep Cycle Batteries - popular brands such as Optima, Ritar, Hard Core and Full River come in various shapes and sizes, the most common being 100 and 120A hr.

Deep Cycle Batteries are the opposite to a start battery, they are designed to run constant low current devices such as lights and compressor fridges, can be discharged to 10.3volts with no damage and recharged as required, typical charge rate is 14.4volts, they can be used to jump start in an emergency but constant use will cause battery to overheat and fail.

There are 2 main types of Deep Cycle Batteries

1. AGM (A Glass Matt) fastest recharge rate, can be put almost anywhere in any orientation, must be used indoors as they are fully contained, they don't like excessive heat.

2. Lead Acid Deep Cycle, used where an AGM cannot be used, under the bonnet of a vehicle, not quite as fast recharge rate as AGM.


Start Batteries - Dozens of shapes and sizes, most of them vehicle specific to each make and model of vehicle due to the mounting position and brackets.

Start Battery are designed to remain constantly fully charged to provide high power to a starter motor, then be immediately recharged ready for next start, the start battery then acts as referance point for the car to run off the alternator. These batt do not like being discharged below 11.5volts and incur damage if this is done. Typical Charge Rate 13.5-13.8volts. NEVER remove a battery from a running car, it will cause damages to computers and equipment as alternators voltages can go as high as 20volts with no referance (battery connected).


Marine, Hybrid, Calcium Batteries - Dozens of brands and sizes avaialble, typaclly used in boats.

Marine or Hybrid Batts - A combination battery, usually of calcium build which can both start and be used for aux. items, generally used in boats, these can be discharged to around 11 volts, any lower and they are very hard to recharge. Much slower recharge rate than a deep cycle.