How we use our caravan batteries and the expectations we place on them are very different to that of a 12v car battery, so it is important to have an understanding of your caravans battery and its associated systems which will generally include solar panels and possibly connections to your vehicle.
Let’s start with explaining the types of batteries:
The most common type of battery used for caravan, camping, marine and automotive would be lead-acid. Why, you may ask? This is due to the high level of reliability coupled with lower associated expenses when compared to other types of batteries. There are 2 main types of lead-acid batteries that delivers a different type of charge:
- Starting & Cranking batteries which offer quick, powerful short bursts of energy on start-up.
- Deep cycle batteries which provide slow and consistent usage over longer periods of time.
You may be wanting to know which charge type is better? This really comes down to the application as this will determine the life expectancy of your battery as well as the performance you can come to expect. Generally speaking, a starting or cranking battery is used for automotive use, whilst caravanners, campers and mariners will use a deep cycle lead-acid battery.
The batteries construction is what greatly differentiates a starting/cranking battery to a deep cycle battery.
A starting/cranking battery, has thinner lead plates inside your battery which help provide a greater surface area of contact between the lead and acid resulting in a reaction that provides more power output and faster recharge times making them ideal for starting or cranking engines. Generally, these types of batteries are used for cars, generators, engines that require short bursts of energy upon start-up. The high output current can be measured by cold cranking amps (CCA). These batteries are designed to be continually recharged, thus holding the maximum capacity charge possible (this is usually between 90%-100% charge). The CCA is more important than Amp hours as it will tell you how much power is in the punch so to speak. These batteries are available in wet cell, gel and AGM battery varieties.
Deep Cycle Batteries:
A deep cycle battery has thicker lead plates resulting in less surface area contact between the lead and acid which is designed to slowly discharge and recharge making it ideal for running appliances such as fridges and lights while camping.
A deep cycle battery refers to the charge and discharge cycle of the battery. Thus, the more you drain/discharge your battery, the deeper the cycle. This is measured in Amp hours (Ah). Designed to be discharged at a low and consistent amperage over a long period. It is recommended that a deep cycle battery be recharged, above or before reaching 20% battery capacity in order for a longer life. These batteries are available in wet cell, gel and AGM battery varieties.
Types of Lead-Acid Batteries
As we have just discussed, both deep cycle and starting/cranking batteries can be categorised into 3 varieties. These are:
- Wet cell (flooded)
- Gel Cell
- AGM (Abosrbed Glass Matt)
The type of battery you choose should suit the correct application in which you wish to use your caravan batteries in order to achieve longer life and improved performance of your caravan battery.
Let’s discuss the differences in the types of lead-acid batteries.
Wet Cell Battery (Flooded)
These batteries are typically your old fashioned serviceable type that are now also available in maintenance free version. The serviceable type allows access to manually test and top up the battery with distilled water when required. The maintenance free version is a sealed unit that simply and automatically tests the effectiveness of your battery via a colour coded sight glass. This does not allow top ups. Wet cell batteries are 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 gel batteries over wet cell and AGM 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)
AGM batteries are leak proof, shock proof, vibration resistant which is why 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 are 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?:
Amp hours are a measurement of your battery’s storage capacity. It will give you an indication as to how long your battery will last, providing that you know the amperage draw of your appliance/s. Thus a 100Ah rated battery will deliver 100 amps of power over a nominated period of time (generally 20 hours). It is 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 typically deliver 100 Amps in normal conditions. It should be noted that if you rapidly discharge your battery that it will become in-efficient, losing up to a third of your total amps. Be sure to check the manufacturer’s specifications of your battery - 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. 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)?
The measurement you require, 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. It is however important to measure 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 and to avoid premature battery life.
WHAT SIZE BATTERY DO I NEED FOR MY CARAVAN?
A very basic guide to selecting your battery size would be to understand and work out your average amp draw from the appliances you plan to run using your battery 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. To calculate the average amp draw from your appliances, please refer to the product manual for manufacturers specifications.
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.
Battery Types Compared
|Battery Types||Cost||Maintenance Required||Engine Bay Mounting||Weight||Vehicle Application|
|AGM/Gel||Medium||No||No||Heavy||AGM- Start/aux Gel- Start AGM|