Lithium battery discharge %

Here’s an update to my Battery Bank kWh article yesterday. Yes, most Lithium batteries can be discharged down to 0% SoC without damage.

My battery bank article yesterday only covered lead-acid and AGM batteries which should not be discharged below 50% State of Charge for best lifespan. However, many modern Lithium batteries can be discharged down to 0% SoC (State of Charge) without damage. This allows a 100 amp-hr Lithium battery to store about 1,200 watt-hrs of energy rather than then 600 watt-hrs of available energy from the same size Lead-Acid or AGM battery that should only be discharged down to 50% SoC for best lifespan.

Here’s more info on Lithium batteries from my colleague Dennis Wieske at Progressive Dynamics

Unless you are very knowledgeable with Lithium technology, I do not recommend building a battery from miscellaneous parts available on line. Instead, purchase a complete battery package – preferably UL approved. These units contain a smart Battery Management System (BMS). The BMS is the brain of the battery controlling the many aspects of charging and discharging of the cells in a battery pack. The unique characteristics of the LFP cell make an ideal replacement for the standard 12-volt automobile battery.

Positives +++++++

• On the plus side, LFP batteries are lighter, can be discharged 100% and will charge much faster than the Lead Acid battery.

• They also have a relatively constant output voltage over most of the discharge cycle.

• Many LFP batteries are rated for 3,000 to 5,000 recharge cycles versus 200 to 500 recharge cycles of a LA battery – so up to 10 times the life of a Lead Acid battery.

• You do not need to connect to a trickle charger while in storage like any Lead Acid or Absorbent Glass Mat (AGM) battery requires. In fact, many manufacturers recommend discharging your battery to 50% while in storage.

• You can also see a significant cost savings over the life of the battery.

• With the help of recycling, we may also benefit our environment compared to Lead Acid batteries.

Negatives - - - - - -

• On the negative side; These batteries are expensive. But while your initial cost is very high, over the life of the battery the cost is actually much lower.

• Most LFP batteries will only provide a discharge rate of two times the rated power of the battery. This may affect the ability to start your on-board generator or power a large inverter to run your air conditioner. In some cases, a super-capacitor is added to provide extra peak current for these situations.

• Charging at temperatures below 32 F will damage the cells.  Some manufacturers are beginning to incorporate methods to protect the cells during lower charging temperatures. The battery will shut off when it reaches 0% of charge. You won’t get a warning unless to have a smart battery monitor.

• LFP batteries require a higher charging voltage (14.0 to 14.6 volts DC) than a standard LA battery charger. So using a charger for an AGM or Lead Acid battery may not allow your Lithium battery to be fully charged.

• Plus, you may need to upgrade other aspects of your RV’s 12-volt charging system. For example, your charger must be capable of providing a continuous output at the recommended voltage for an extended period of time. That means that the wire between the charger and the battery must be of sufficient gauge to handle the extra current and have minimal losses at full power. I would recommend no more than a 2% voltage loss end to end. This includes the charger and battery negative connections to chassis ground.

• You’ll also want to replace a standard circuit breaker with a manual resettable circuit breaker (Bussmann CB 185 series or equivalent) with a rating of 120% of the charger or load current, whichever is higher. Note the Shortstop breaker in your RV is usually rated lower than the original charger.  It won’t take long before it burns out.

• Any portable generator must be capable of handling the full rated power of the charger plus any additional 120 VAC appliances that will be running simultaneously. The maximum recommended load should be no more than 80% of the generator rating.

• It would help to have a battery monitor calibrated for Lithium battery voltages; this will allow you to monitor your state of charge (SOC) to determine if a generator run is warranted.

• Some converter/charging manufacturers may have a Lithium charging option available for charging at 14.6 volts, but it may mean replacing your original unit.

• Progressive Dynamics offers many Lithium options in the current product line. Each of the “ALL IN ONE” power centers offers an option to change from the default Lead Acid setting to Lithium. Each has a converter replacement section for Lithium charging, as well – a requirement for older models.

• There is also a line of deck mount Lithium chargers. Many older units have an option for manual control of the multi-stage “Charge Wizard.” Manual selection of the BOOST mode will provide 4 hours of rapid charging at 14.4 VDC. Progressive Dynamics is committed to providing quality Lithium converter/charging systems.

Final thoughts…

I hope this provides a clear understanding of the requirements and considerations when upgrading to a LiFePO4 battery. You will have many years of satisfying use when you take the time to do the homework first. Don’t forget there are also Solar Lithium options and DC to DC Lithium converters to charge from your engine alternator.

Let’s play safe out there… Mike Sokol