This is a question we get asked every day by the general public. Lithium deep cycle marine batteries are not like lead acid and not all battery chargers are the same.
A 12v lithium LiFePO4 battery fully charged to 100% will hold voltage around 13.3-13.4v. Its lead acid cousin will be approx 12.6-12.7v. A lithium battery at 20% capacity will hold voltage around 13V, its lead acid cousin will be approx 11.8v at the same capacity. As you can see, we are playing with a very narrow window of voltage with lithium, less than 0.5V over 80% capacity.
A Lithium LiFePO4 charger is a voltage-limiting device that has similarities to the lead acid system. The differences with Li-ion relate to the higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. Whilst lead acid offers some flexibility in terms of voltage cut off, manufacturers of LiFePO4 cells are very strict on the correct setting because Li-ion cannot accept overcharge. The so-called ‘miracle charger’ that promises to prolong battery life and gain extra capacity with pulses and other gimmicks simply does not exist. LiFePO4 is a “clean” system and only takes what it can absorb.
Lithium chargers are based on a CV/CC (constant voltage/constant current) charge algorithm. The charger limits the amount of current to a pre-set level until the battery reaches a pre-set voltage level. The current then reduces as the battery becomes fully charged. This system allows fast charging without the risk of over-charging and is suitable for Li-ion and other battery types.
Enerdrive’s ePOWER Lithium Charger Algorithm
As you can see from the above charge graph, the lithium battery has a steep rise in voltage at the very end of the charge cycle. At this stage the charge current drops extremely quickly and the charger then switches to power supply mode.
The majority of the lead acid smart chargers these days have specific charge algorithms to suit Flooded/AGM/Gel batteries which generally require a 3 stage charge process, Bulk/Absorption/Float. Once the charger enters the bulk state, it will normally charge a lead acid battery at full current to approx 80% capacity. At this point the charger will transition to the Absorption stage.
Ultimately, using a battery charger with a specific Lithium charge algorithm is the best option for maximum performance and lifespan of any lithium battery.
One of the greatest leaps in battery technology over the past couple of years have been these added features, and they are complete game changers for many of us who rely on solar energy year-round, such as the scenario above. To compensate for the temperature limitations of LFP batteries, some have a self-heating feature which keeps the battery core temperature above 41° F, so it will work throughout the year no matter how cold it gets outside! This self-heating feature does use a bit of the battery’s stored energy, but it’s worth its weight in gold for those who live in colder climates. On the other hand, Smart Energy Saving Mode is a new feature available on Renogy’s 24V battery line, as it automatically switches into this mode within 30 seconds if the system finds that the battery is not charging or discharging.