QUESTION: I enjoyed your column last month on dual-battery systems. I was particularly interested in your statement that a high-cycle battery might be a better option than a deep-cycle. This goes against all of the advice I’ve heard so far, which is why I’m keen to hear more about battery selection and what should be considered when one is shopping around for an auxiliary unit.
ANSWER SUPPLIED BY: National Luna
Tel: (011) 452 5438
National Luna: The subject of auxiliary-battery selection can be a minefield of data, facts, and uninformed opinions. This situation is made worse by the retail sector, in which well-meaning salesmen (with limited knowledge and battery training) make the mistake of recommending their top-selling product as a one-size-fits-all solution. More often than not, this is a deep-cycle, wet-cell / flooded battery.
Another problem with the battery market is that there is little (if any) information on how various batteries perform under different charging conditions. Unfortunately, most manufactures don’t want this information publicised, as it might reveal too much about their product’s performance.
Ironically, battery selection is often the area that most people merely glance at before focusing their attention on the dual-battery system itself, believing that an expensive isolator and/or DC-to-DC charger will solve all their problems. The truth is that more than 80% of all dual-battery problems have nothing to do with the split-charging system, and almost everything to do with the type of battery you’ve selected.
“More than 80% of all dual-battery problems
have nothing to do with the split-charging system,
and almost everything to do with the type
of battery you’ve selected”
In other words, if your dual-battery system isn’t working as planned, the chances are high that your auxiliary unit doesn’t match your intended application.
As mentioned before, it’s often the industry norm to simply fit a flooded deep-cycle product; but, in most cases, such a battery will take up to 24 hours to reach a 100% recharged state even under optimum charging conditions. This is obviously not ideal for most overland travellers who drive far less than that on an average day. Other factors, such as the alternator’s output, will also have a significant impact on the battery’s recharge rate.
This is why we sometimes recommend the use of a high-cycle battery instead of a deep cycle unit. Sure, the high-cycle won’t last as long, or offer as much usable energy; but it will recharge considerably faster than a deep-cycle version, and therefore, it’s often a more practical solution.
However, we’re not suggesting that a high-cycle battery is the final answer for dual-battery systems. We’re simply saying that (in some instances) it may be a better option. Ultimately, the battery you choose should be the one that best matches your charging set-up, and this should take the following into account:
- Which split-charging system you are using (DC-DC or solenoid)
- Your vehicle’s alternator output, or operating voltage, is critical (most batteries will not charge with low voltage)
- Your typical driving time
- What are your daily power-consumption needs, and
- Whether or not you have a solar-system installed.
Typically, you should start your auxiliary battery quest with three questions:
- What is my budget?
- What are my size restrictions?
- What battery design / technology best suits my needs?
This raises the subject of specialist batteries, which are slowly migrating into the 4×4 recreational industry. The following information highlights the pros and cons of three auxiliary battery options that are readily available to the overland travel market.
THE FLOODED (WET-CELL) LEAD ACID BATTERY
These feature free-flowing liquid electrolytes that tend to heat up when recharged. The resultant heat causes evaporation and a loss of water, so regular servicing and maintenance is required. What’s more, flooded lead acid batteries are considered hazardous technology, due to off-gassing and the potential of spilling. Although they’re widely available, and their initial cost is comparatively low, flooded lead-acid batteries require maintenance when it comes to inspection, servicing and storage. What’s more, because a flooded battery will automatically discharge up to 10% per month, it’s vitally important that this battery type be connected to a maintenance charger when not in use.
THE GEL BATTERY
This is a sealed (valve-regulated) lead acid battery that is not subject to spilling, and is maintenance-free. Gel batteries generally have thinner plates, and the electrolyte mixture features an additive that creates an almost gel-like consistency. The drawback of Gel batteries is that they require precise charging, a slower charging rate (voltage and time), and that they are easily damaged when overcharged. An even more crucial point, is the fact that gel batteries are extremely sensitive to heat, and should never be mounted in a location where they’re exposed to an ambient temperature exceeding 25ºC. This includes engine-bay applications, or even in the back of a hot SUV parked under the African sun.
THE AGM BATTERY (ABSORBENT GLASS MATT)
Also a sealed (valve-regulated) lead acid battery that’s maintenance-free; however, the big difference between an AGM battery and a Gel battery is that the electrolyte mixture is not a gel substance. Instead, the AGM battery uses matted glass-fibre separators in which the electrolyte mixture is trapped. In most cases, an AGM battery will recharge faster than a flooded battery; but, because of the thinner plates, the AGM won’t handle a discharge rate greater than 50%. Users may have to replace the battery more often, because of their potentially shorter life span.
THE AGM EV TRACTION DRY-CELL BATTERY
This battery boasts the thickest plates of the four units listed here; it also has the higher density of active materials, which results in better performance, greater capacity, and a longer lifespan. Dry-cell batteries are also completely sealed and maintenance-free, and they recharge quickly. The downside is that most dry-cell batteries are expensive; but, when you consider their performance and total working life, they can offer good value for money in the long run.
You’ll find more information and technical specifications at the following websites:
In a later column we’ll cover 6 dual-battery installation mistakes you’re most likely to make. Join our free newsletter below for future dual-battery posts.