Caravan & RV Batteries Explained
When we are talking Caravan, Camping, Marine or Automotive, Lead-Acid type batteries are by far the most common type of battery used. This is mainly due to the ratio of higher reliability and lower expense compared to other types of batteries. Whether you have A Gel, AGM (Absorbed Glass Matt) or Wet Cell, they are all constructed to deliver a charge in 2 ways, either quickly and powerfully or slow and consistently. The better you can suit your battery correctly with your application, the longer life and better performance you will achieve.
There are 2 Main Types of Lead-Acid Batteries:
It is the batteries construction that differentiates a Starting/Cranking and Deep Cycle battery.
For a Starting/Cranking battery, thinner lead plates inside your battery help to provide more surface area contact between the lead and acid resulting in a reaction that provides more power output and quicker recharge times – ideal for starting or cranking engines.
Deep Cycle batteries have thicker lead plates resulting in less surface area contact between lead and acid which is designed to slowly discharge and recharge – ideal for running fridges and lights while camping.
Hybrid batteries combining the best of both worlds are available and do serve a purpose, but for better performance and a lot longer comparative battery life, try to suit the correct battery to the correct application.
These batteries are designed for high output current which can be measured by CCA (cold cranking amps) and generally used for cars, generators, engines or anything else that requires short bursts of high energy on start-up. Designed to be continually recharged holding the maximum capacity charge possible (usually between 90-100%). The capacity of the battery can still measured in Amp Hours, but the CCA is more important as it will tell you how much power is in the punch - so to speak. These batteries are available in the Wet cell, Gel cell and AGM varieties.
Deep Cycle Battery
Deep cycle refers to the charge and discharge cycle of a battery. The more you drain/discharge your battery, the deeper the cycle.
Measured in Amp Hours (AH) and designed to be discharged at a low and consistent amperage over long periods. These batteries are great for running fridges, lights, stereos or anything else that has a consistent but relatively low amperage output. Recommended to be recharged above or before 20% battery capacity for a longer life. You can still measure the CCA (Cold Cranking Amps) of a deep cycle but this is of less importance in deep cycle applications and therefore have considerably lower CCA than in Cranking/Starting Batteries. These batteries are available in the Wet cell, Gel cell and AGM varieties.
Different Types of Deep Cycle and Starting/Cranking Batteries
Both types are designed for different applications and can be categorised into 3 sub types:
Wet cell (flooded)
AGM (Absorbed Glass Matt)
Although all of these types can be considered ‘all purpose’ batteries that will work to an acceptable level in different applications, for longer life and better performance of your battery, it is better to suit the correct battery type with the correct application if possible. For e.g., (a deep cycle battery designed to run your relatively low amperage portable fridge for extended periods without continual charge, will have a considerably longer life than trying to use it to crank your car engine over day in day out and vice versa).
Wet Cell (Flooded) Battery
Whether used for a deep cycle or starting/cranking application, these batteries are typically your old fashioned serviceable type that now come in maintenance free version as well. The serviceable type allow access to manually test and top up the battery with distilled water when required. The maintenance free version is a sealed type unit that simply automatically tests the effectiveness of your battery via a colour coded sight glass (but does not allow top ups). An inexpensive option compared to Gel and AGM, but generally are not as versatile due to their liquid contents and do not last as long as their technological advanced counterparts.
The Gel cell has a silica additive that effectively turns the acid inside your battery to a jelly like substance, the advantage of this over other types of lead acid batteries is that it is the most effective for ‘deep cycle’ applications, especially in hot weather applications. These batteries are also designed to be leak, shock and vibration resistant. The disadvantage is that it is the most expensive lead-acid type battery and can become very sensitive to overcharging, hence the correct Gel type battery charger must be used to prevent poor performance and premature battery failure. While Gel Cells are considered the best for continual deep cycle applications, AGM (Absorbed Glass Matt) technology is rapidly taking over the role of Gel Cells due to their all-round performance and price in comparison.
AGM (Absorbed Glass Matt)
Leak proof, shock proof, vibration resistant, these batteries are generally considered the pick of the bunch as far as Caravan, RV and Camping applications are concerned. An Increased discharge and recharge efficiency compared to wet cells and less sensitive to over-charging compared to Gel types, these batteries tend to last longer and perform better overall - Especially when consistently kept above a 50% battery capacity long term. The current AGM battery price point definitely makes this a value for money option worth considering.
What does battery ‘Amp Hours’ mean?
In a nut shell
Amp Hours are a measurement of your battery’s storage capacity. It will give you a guide as to how long your battery will last providing you know the amperage draw from your appliance. A 100AH (Amp Hour) rated battery will deliver 100 Amps of power over a nominated period of time (usually 20 hours).
It is worth noting and important to consider that the total time of discharge and the amperage drawn is not a linear relationship. The slower the discharge rate the more efficient your battery will be. For this reason manufacturers have come up with a ‘standard’ to base their Amp Hour rating, which is generally over a period of 20 hours. This means that over a discharge period of 20 hours, a 100AH battery will deliver 100 Amps in normal conditions. Over a longer period of say 100 hours, this same battery can potentially provide up to 120 Amps of power due to the efficiency of a slower discharge but it is still only classed and rated at 100AH at 20 hours.
Don’t be fooled…
If you rapidly discharge your battery it becomes horribly in-efficient losing up to a third of your total Amps. For e.g., (A 100AH battery discharged rapidly over 1 hour, will only provide approximately 65% of the total capacity or in this case 65 Amps of power, not the 100 Amps as rated at 20 hours) Be sure to overcompensate on battery size and rating if you will be rapidly discharging your battery. Also it is worth noting that some manufactures will rate their batteries over a longer period than the standard 20 hours to give a technically true, but misleading higher (AH) Amp Hour rating. Be sure to check the manufacturer’s specifications - Especially on cheaper lessor known brands entering the market.
What does CCA (Cold Cranking Amps) mean?
Cold Cranking Amps (CCA) is a measurement that defines a battery’s discharge capabilities.
In other words - The power in the punch so to speak! The battery’s ability to supply power or start something like an engine which needs high volumes of power quickly, the higher the CCA, the more power it can supply.
Manufacturers generally stick to a standard to measure CCA. Batteries are subjected to a pre-defined temperature of 0 Degrees Celsius and discharged for 30 seconds while maintaining a minimum of 7.2 volts total. The total amps delivered in that time will determine the CCA rating of the battery.
The higher the CCA rating, the higher the starting power of the battery. This is important for high power requirements used in short bursts like cranking engines. The trade-off is that high CCA batteries are less effective in deeper cycle applications. Although technically a Starting/Cranking battery will work in a Deep Cycle application and vice versa, for longer battery life and better performance, it is important to suit the correct battery to the correct application.
Why are some Batteries Rated in Amp Hours (AH) and some in Cold Cranking Amps (CCA)?
It all depends on your application, Deep Cycle Batteries are measured in Amp Hours and Starting or Cranking Batteries are measured in Cold Cranking Amps.
Deep Cycle Applications require a power measurement that can tell you your battery capacity, so you can theoretically work out how long your battery will last before needing to recharge. This is defined as Amp Hours, a 100AH battery will theoretically provide 100 Amps of power. (Manufacturers calculate the AH rating over a discharge period of 20 hours)
Starting or Cranking batteries are designed to deliver short bursts of high power that is continuously being recharged. It is not therefore considered relevant to know how long your battery will last as its only designed to be discharged for less than 30 Seconds at a time before being recharged. Therefore the important measurement is the amount of power being delivered in that short time of 30 seconds, which is defined as CCA (Cold Cranking Amps)
It is important to use the correct battery for the correct application to get the best performance and life out of your battery. (Premature battery life will otherwise result)
What Size Battery Do I Need for my Caravan?
A very basic guide to selecting your battery would be to understand and work out your average amp draw from your appliances (found in manufacturers specifications) and multiply this by the length of time in hours you require power. This will give you an approximate total Amp Hours required from your battery.
For example: Say you have an appliance that has an average Amp draw of 5 Amps per hour. You want run this setup for 20 hours without the use of a charger. (20 hours X 5 Amps per hour = 100AH) You would theoretically need a 100AH rated battery.
Of course there are many factors that will influence the ACTUAL Amphour output of your battery that often results in less Amp hours than the manufacturers rating. It is best to over-estimate your battery requirements by at least 20- 50% as an absolute minimum.
Factors you need to consider
Connecting a charging system (solar panel/generator/mains power operated) will top up your battery reducing the total overall battery capacity needed. A 10 Amp / hour charger will give you an extra 100 Amps over 10 hours that you can factor in.
The typical Lead-Acid battery used in the Caravan Industry is rated accurately over a 20 hour discharge. Rapidly discharging your batteries over very short periods can reduce your Amp Hour rating by up to 35% (on a conventional 100AH, rated at 20 hours battery, 65 Amp hours may be a more accurate amp hour rating over 1 hour discharge)
Temperature! As a general rule the warmer the better for efficiency, with approximately 27 Degrees being the optimum temperature for accurate Battery Amp Hour rating results.
Voltage Drop. The longer your cables, the more voltage drop will occur. Potentially this can increase the duty cycle duration of some appliances, meaning the motor has to run longer to achieve the same result draining your battery quicker.