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Power Converters and Deep Cycle Batteries
When discussing power converters for charging batteries, I feel it is vitally important to mention the type of batteries used for an RV and how they need to be charged. While the complete guide to leisure batteries is the topic for an entirely different article, it is important to look at these batteries in the context of a power converter.
The reason for this discussion revolves around the growing popularity of lithium ion batteries. The question often arises: “can I charge my lithium ion batteries using a power converter?”. This also applies to conventional 12V battery chargers.
Technically, you can charge any battery rated at 12V with a DC power supply of the same voltage. However, it is not recommended to charge lithium ion batteries with a charger designed for lead acid, AGM, or calcium gel batteries.
Until fairly recently, all batteries used for deep cycle applications, like an RV, have been mostly lead acid flooded type batteries. These batteries use lead plates, immersed in an acid bath, using distilled water for cooling. Absorbent Glass Mat (AGM) batteries provide better cooling and can last longer when used for deeper cycles. Calcium and other types of gel batteries can be better than flooded lead acid batteries in terms of cooling. This is just a basic description of typical deep cycle batteries. The important distinction to be made here is that all these batteries have the same charge cycle.
In the previous section, I spoke about the various stages of battery charging for deep cycle batteries. These would be high voltage bulk charging, lower voltage absorption charging (when the battery reaches approximately 80% charge capacity), and a float charge at low amps to maintain battery voltage. This is ideal for all lead acid, AGM, and gel batteries. They require a high voltage initially and it is important to provide a float voltage because these batteries are prone to self-discharge which, left unchecked, will deteriorate the battery.
Lithium ion batteries have an entirely different cell type and use a different charge cycle, known as constant voltage / constant amperage charging (CV/CC). This distinction is of great importance. The battery charging voltage for lithium ion batteries is the opposite to conventional deep cycle batteries. The initial charge remains fairly constant at an average 13.5V, contrary to deep cycle chargers that provide a bulk charge stage of around 14.4V. The lithium ion charger will provide a short high-volt (±14.4V) peak charge at the end of the charge cycle with greatly reduced amperage. The charger will shutdown all current when the battery reaches 100% charge to prevent overcharging, whereas a deep cycle charger will continue providing a trickle float charge.
Because conventional deep cycle batteries remain the most common, most power converters are designed to provide the ideal charge stages for these batteries. If used for a lithium ion battery, this type of charge cycle will damage the battery. The charge voltage will be the opposite, to that required for optimum charging. More importantly, the continues float charge once the battery has reached 100% capacity, will result in over charging lithium ion batteries.
Using lithium ion batteries, charged by a conventional power converter, will result in reduced battery power output and a shorter lifespan.