BATTERY CHARGING GUIDE - Everything you need to know about Charging Deep Cycle Batteries and Charging AGM Batteries.
Battery Charging Bulk, Absorption, and Float Charge
Battery charging occurs in three stages; bulk, absorption and float charge. Bulk charge refers to the first stage of the battery charging process, in which the rated maximum current is sent to the battery while maintaining a constant voltage.
After this comes the absorption charge stage, which sees the voltage gradually lower as internal resistance increases. The final float charge stage occurs after the battery reaches its full charge and the charging voltage is reduced. This process is often referred to as a ‘maintenance’ or ‘trickle’ charge and is intended to keep an already charged battery from discharging.
Solar charge controllers are also able to perform this function by sensing voltage drops in the battery and sending short ‘pulses’ to prevent loss of charge. A ‘pulse’ is a very short charging cycle and may occur several hundred times per minute. Although AGM Deep Cycle Batteries self-discharge at a lower rate than standard lead-acid batteries, they will still require this type of ongoing maintenance charge or at least monthly top-ups to avoid damage.
How does a battery charger work?
The deep cycle battery charger has three main jobs: getting a charge into the battery, optimizing the charging rate and stopping when the battery has reached full charge. Smart chargers work with most battery types and use the battery’s voltage to detect the type of battery and charge needed.
Look for a smart charger that also comes with reverse pulse technology as this can help reduce battery temperature when charging. If you are not using a smart charger to charge your 12V deep cycle batteries, the charging current should be at least 10% of the amp hour rating for a flooded lead-acid battery or up to 30% for an AGM lead-acid battery. Find out more about choosing a deep cycle battery charger.
Battery Charging Time
Charging time is the time it takes for the reconstitution of the battery’s active chemicals to be completed while the cell temperature is kept at a safe level. This process stops when the termination voltage has been reached To avoid overcharging.
The charging time for deep cycle batteries depends on the number of amp-hours its stores. Divide the amp hour rating of your battery by the amp rating of the charger and you’ll have an estimate of the time needed to reach full charge. For example, a 100 amp hour battery at a 50% stage of charge (50 amp hours) would take approximately five hours to charge on a ten amp battery charger.
It’s important to avoid overcharging as this can cause grid corrosion and severely reduce battery life. The excessive heat this creates can also cause the plates within the cells to buckle and shed their active material. Using a smart charger can help avoid the problem of overcharging as it will automatically switch off when the correct level of charge has been detected.
Charging Your Battery from Solar Panels
Investing in solar panels will allow you to charge your deep cycle battery with free energy from the sun, even when away from mains power. After panels have been placed in the sun, they will need to be attached to a solar regulator, also known as a charge controller. 12-volt solar panels can produce fluctuating power that would damage a battery if left unregulated but the solar charge controller keeps this voltage at a safe level. Most solar regulators also have the technology to switch to float charge when the battery has reached full capacity; eliminating the problem of overcharging.
While charging from solar is dependent on the weather and can involve an initial setup cost, solar panels provide an inexhaustible and environmentally friendly energy source for your batteries.
Many of the latest MPPT (Maximum Power Point Tracking) solar regulators can provide up to 97% efficiency, which is a big improvement on older style regulators. This can be an advantage where space is tight and a larger panel is not an option.
Charging From Your Vehicle Alternator
In general car or van alternators work reasonably well with Lead Acid and AGM batteries. They are not the ultimate battery chargers however and will never fully charge a Deep Cycle battery, so its best to use a battery charger when mains power is available to top up the battery charge and avoid reduced battery life from sulphation.
Also, it is important to note that alternator output voltages are often reduced by cable/wiring runs and Dual Battery systems so care needs to be taken to measure the actual voltage received at the battery across its terminals to ensure its adequate to charge the battery fully.
Conversely for Gel batteries fitted close to the alternator (under-bonnet with a thick gauge cabling) there is a real risk of damage due to over-charging as the alternator output can be too high for the battery.
Charging From Your Generator
Many Portable Generators do not have battery charging circuitry built-in and should be used with care if they provide a DC outlet (although you could plug a battery charger into the 240V socket, its a fairly inefficient way to operate unless you really need to). The later models (from Honda etc.) with the built-in chargers can provide a reasonably quick and efficient battery top-up on sites where they are allowed (or when off-site), although many users do grow tired of the noise and migrate to solar over time.