Auxiliary Battery Systems

Whether in our personal or professional lives, we’ve all experienced that dreaded occasion to where the car battery is dead, or as the English put it… “flat”. In our personal lives this occasion is mostly a nuisance, but it’s quite a different story in our professional lives especially for those of us with critical jobs in public safety, utilities, towing, etc. A dead battery in these professions can literally put lives at stake.

Despite the critical nature of jobs such as public safety, it never ceases to amaze me how increasingly common dead batteries are. In many occasions those dead batteries can simply be chalked up to poor maintenance of terminals, replacements and belt tensions. Others are the result of phantom current draw from the myriad of electronics that constantly sip battery power, even when if the switch is off. Another major reason for flat batteries are technicians maxing out the specified load and not understanding the vehicles charging capability is never constant.

Along with performing proper vehicle maintenance to prevent dead batteries, another great way to mitigate problems is using an auxiliary battery. The use of an auxiliary battery is especially recommended for missions that require operating electronics for extended periods with the engine off, i.e. emergency management, bait cars, drop cars and surveillance vans. Regardless of the mission, on-board electronics should be connected to the auxiliary battery which leaves the vehicles starting battery fully dedicated for normal usage. As a result, starting batteries tend to last longer in terms of years and the auxiliary battery can play a dual role by providing emergency power should the starting battery ever battery fail.

To get the most out of auxiliary batteries and to keep operators safe, there are some simple things you should consider and recommend items you should include in any installation.

1 – Battery Isolator
Perhaps the most important item needed for an auxiliary battery system is a battery isolator. Isolators allow auxiliary batteries to receive a charge from the vehicles electrical system but as the name suggest, isolates it and prevents a back-flow of current and depletion of the auxiliary battery. Advanced battery isolators also give operators the ability to manually override isolation and to assist with emergency jump starting.

2 – Fuses
When adding an auxiliary battery system, a new a circuit is created and in some cases such as a surveillance van, many sub-circuits are created as well. Without compromise, anytime a new circuit is added, proper fusing needs to be installed. For auxiliary battery systems, in general I recommend using a master or a.k.a. limiter fuse in between the auxiliary battery and the vehicles electrical system. Additionally, any sub-circuit originating from the auxiliary battery should have its own dedicated fuse. Fuse sizes are dependent upon total load or in other words amperage demand that will be placed up the new circuit(s) and potential use. For example, an auxiliary system designed to support 40 amps worth of electronics and the potential emergency jump start, should probably use a 150 amp limiter fuse and a separate 50 amp fuse for the sub-circuits. In essence, the fuse size must be larger than the demand by a small margin.

3 – Wiring
Like fuses, the size of wiring will be dependent upon the total load and potential future use. Also like fuses, if the wiring is too small… it will simply burn up, but in this case pose a serious safety hazard. On that note, the bigger wire size (gauge, AWG) the better.

4 – Battery
A perfect battery type to cover various mission needs is an SLA battery (sealed lead acid). SLA batteries are resistant to vibration can be mounted in any orientation, endure temperature extremes and provides a long shelf life for energy. When it comes to battery size, there are a lot to choose from and here again; it will be dependent upon use. Like wiring, get the largest size possible or that the vehicle storage space will afford. The larger the size, the longer it will be able to support operation with engine off and the better it will be able to provide emergency starting power. For reference, SLA batteries are rated in amp hours (aH) which indicates how much amperage it can deliver in a given hour before depletion. A great battery for initial consideration that can serve many application needs is a 60aH battery.

Regardless of the aH rating chosen of an SLA, I highly recommend purchasing a battery with a high maximum discharge rate especially when the potential use for emergency jump starting exist. A battery with maximum discharge rates of 300 amps and higher are an excellent choice. A rule of thumb, SLA batteries with nut & bolt type terminals typically have a desired discharge rate needed for safe jump starting.

Another battery type worth considering is deep cycle marine batteries due to large capacity and ability to sustain high levels of depletion. However, marine batteries are typically larger, not as tolerant to shock and unusual orientations like SLA batteries. A notable exception to the norms of marine batteries, are those offered by Optima which are significantly more rugged and better apt to handle the rigors of public safety driving.

5 – Location
When situating auxiliary battery systems, they can be located nearly anywhere that is practical for mission needs. With some exception, I recommend avoiding placement of gear inside the engine compartments due to excessive heat and of course, lack of space. The most likely spot for sedans are trunks and possibly underneath rear seats. For trucks with limited cargo space, a bed mounted tool box should be considered. Where ever the system is installed, much care should be given to ensure batteries are securely fastened to avoid spillage, short circuits and becoming a heavy projectile during accidents.

6 – Difficulty
In my estimation, installing an auxiliary battery system is easier than installing a car stereo. However, as mentioned there is serious risk involved if done improperly. The whole purpose of an auxiliary system is to avoid risk and to provide great mission capabilities. So I do recommend that before undertaking such an installation that one holds at least basic automotive electrical skills and mechanical aptitude as minor vehicle modification will no doubt be required.

7 – Cost The initial cost of a well-furnished auxiliary battery system should be approximately $600.00. When the benefits are factored in such as eliminating cost associated with emergency jump starts, early battery replacements, equipment failures due to low & high voltages and the new ability to operate electronics without engine power, the net cost could be $0.00 very quickly.

Thanks for reading,

Jake