Lithium Boat Batteries: Are they worth it over Sealed Lead Acid?

Lithium batteries are on the rise in fishing, flounder gigging and bowfishing boats; despite their higher cost. The leading reason for the switch is that lithiums are advertised to last significantly longer than lead acid batteries, but many fishermen might see this as an advertising gimmick and don't completely understand what this means. 

Many people, including myself initially, are confused why a 100 amp hour deep cycle battery and a 100 amp hour lithium battery have different run times. This made absolutely zero sense to me, so I decided to do a bunch of research and contact various manufacturers of each type of battery to better understand the actual differences so I can better explain them to other curious fishermen like myself. So, if you want to know the technical differences between lithium and lead acid batteries, keep reading! 

Let's dive into the seven core battery characteristics, and how lithium and lead acid batteries compare according to these. 

Seven Core Battery Characteristics: How They Compare

These seven characteristics are cycle life, expected battery voltage, depth of discharge, how fast it takes to fully recharge, efficiency, battery weight, and maintenance. 

Cycle Life

The cycle life of a battery refers to how often it can be discharged and recharged.

• A typical sealed lead-acid battery can be discharged and recharged between 500 and 800 times in its life. 
• A typical lithium ion phosphate (LiFe PO4) battery can be discharged and recharged between 2000 and 5000 times in its life.
• Based on cycle life, lithium batteries will last approximately 4-5x as long as sealed lead acid batteries.
• Many sealed lead acid batteries come with a one-year warranty, while similar lithium batteries come with 5-10 year or more warranties. 

Expected Battery Voltage

The battery voltage can fluctuate depending on how much charge is remaining on the battery. A 12 volt lithium and lead acid battery actually output different voltages when fully charged and when completely discharged. 

• A lead-acid battery will output a voltage of roughly 12.89 volts when fully charged, and will discharge down to less than 11.6 volts. 
• A lithium iron phosphate (LiFe PO4) battery will output a voltage of approximately 14.4 volts when fully charged, and can drop to 10 volts when completely discharged. However, the lithium battery will stay above 12-12.5 volts for over 90% of the discharge cycle. Due to this - we recommend considering a voltage regulator on your lithium batteries to keep from damaging 12 volt accessories. 
• Note: A 12 volt battery that reads a voltage of 12 volts is actually considered to be fully discharged, or a "dead battery". 

In this particular case, lead acid batteries are actually better than lithiums because of the initial extremely high voltage a lithium battery can output. At 14.4 volts, many standard electronics designed to run on a 12 volt system can be fried or burn out. For example - our Swamp Eye Submersible and Mini Swamp Eye Submersible Lights. If you run these lights, or similar equipment that is 12 volt only - you must install a voltage regulator onto your lithium batteries. 

On the flip side, lead acid batteries stay within the expected range of 12-13 volts. Some lead acid batteries may even reach 13.6 volts on the high end, but this is the ceiling for what's acceptable on a system that operates on 12 volts. 

Depth of Discharge

The depth of discharge refers to how deep you can discharge a battery before you have to recharge, or else you may damage the battery.

• A typical lead-acid battery has a 70-80% depth of discharge, meaning you can discharge the battery until you have 20-30% of the battery charge left. 
• A typical lithium ion phosphate (LiFe PO4) battery has a 91-95% depth of discharge, meaning you can discharge the battery to 5-9% of the remaining charge while continuing to operate your accessories. 
• A lithium battery can be discharged to 0% charge, and then be recharged without effecting the life of the battery. On the contrary, doing this to a sealed lead acid battery may damage the battery. 
• Anotherwords, a 100 amp-hour lead acid battery may perform similarly to a 70-80 amp hour lithium battery in terms of depth of discharge. 

In the table above for "Expected Battery Voltage" you can see the expected voltage output of a lithium compared to a lead acid battery. This is the best indication of your depth of discharge. The lithium battery will output 12.5 volts even when it's at 10% charge, whereas a lead acid battery is below 12 volts at the 30% remaining charge mark. 

How Fast it Takes to Fully Recharge Battery

The charging rate is how fast it takes batteries to go from a low charge to fully charged. 

• Sealed lead acid batteries can be charged in 12-16 hours with a standard trickle charger, or as fast as 8 to 10 hours with a multi-stage charger that fluctuates charging amperage to achieve a faster, full charge.
• Lithium ion phosphate (LiFe PO4) batteries can charge in as little as 3 to 4 hours. Many lithium batteries also have an app for your phone to check how much charge is left on a battery.

Efficiency

The efficiency of a battery refers to how much power the battery stores and how much of that power you can actually utilize.

• When you put electricity into a lead-acid battery, you will lose approximately 10 to 15% of the power when you attempt to take that power back out of the battery. Anotherwords, you have to put more energy into a lead-acid battery than you will be able to retrieve back from the lead-acid battery. 
• When you put electricity into a lithium ion phosphate (LiFe PO4) battery, you will lose less than 2% of that power when you attempt to retrieve it from the battery. Another words, lithium batteries are nearly 98% efficient in storing and discharging energy. 

Battery Weight

In terms of boating, fishing, bowfishing and flounder gigging; weight is everything. This is where lithium iron phosphate (LiFe PO4) batteries greatly benefit. 

• A typical 100 amp hour sealed lead-acid battery weighs approximately 70 lbs
• A typical 100 amp hour lithium iron phosphate (LiFe PO4) battery weighs approximately 31 lbs. 
• Lithium iron phosphate (LiFe PO4) batteries are less than half the weight of conventional lead-acid batteries. 

As you may already know, weight is everything on a boat. Weight can determine how shallow you can run and it can determine how big of a motor you need to achieve your top speed. Lithium batteries (100 amp hour) can reduce weight by approximately 40 lbs per battery when compared to a sealed lead acid battery (100 amp hour). 

Maintenance

Battery maintenance refers to making sure your batteries are conditioned (this can be done with a typical on-board battery charger).

• Lead acid batteries can be maintained with typical on-board chargers that manage the batteries charge and conditions the battery as needed. This allows the battery to last as long as possible.
• Lithium batteries can be easy to maintain, especially if the battery comes with a battery management system that basically acts the same as an on-board charger for lead acid batteries. If your lithium battery does not have this, then just make sure the battery charger you choose is marked as lithium compatible or it could damage the battery. 

Boat Battery Comparison Summary: Lithium vs Sealed Lead Acid

In summary, lithium ion phosphate (LiFe PO4) batteries have every advantage over sealed lead acid batteries, with the exception of the high initial voltage output for a fully charged lithium ion battery. If your electronics are voltage sensitive, such as "12V only" for a 12V battery, then we do not recommend charging your lithium batteries to a full charge without using a voltage regulator. Sealed lead acid batteries have no problem with this, but a fully charged lithium battery can damage 12V components when outputting 14.4 volts. 

We do not recommend using fully charged Lithium Ion Phosphate batteries with our Swamp Eye Submersible or Mini Swamp Eye Submersible lights without a voltage regulator. These lights are capable of receiving up to 13.6 volts and will be damaged if a fully charged lithium battery outputs more than this. 

On the contrary, our Swamp Eye Gen 2.X Light Bar and our Swamp Eye HD Bowfishing Lights are lithium compatible due to their ability to adapt to more flexible voltage inputs. You can run these bowfishing lights on 12 volt or 24 volt lithium batteries. 

IMPORTANT NOTE REGARDING LITHIUM BATTERIES:

We have had customers who work for landfills inform us that when lithium batteries are damaged during the compaction process, they can cause uncontrollable fires that will literally burn underwater. This is important to keep in mind as a safety precaution - lithium batteries should be carefully cared for and stored in a protected area. If they are compromised while on your boat, it can result in a very dangerous situation. 

We are not trying to sway you one way or another in terms of which boat batteries to choose, we just want to offer research and feedback we have learned from various customers, manufacturers, and boat battery users. We are not experts on either type of battery, we are only presenting information that we have learned from others and our own experiences.