Oversized lithium batteries: will they hurt my recreational application?

When looking at power sport and recreational applications, we generally think about starting applications. This could be starting the engine for a jet ski, snowmobile, dirt bike, side-by-side, or similar vehicle. However, other recreational applications include deep cycle applications. like trolling motors in boats or house lights for RVs. In this blog we will be addressing over-sizing batteries for both starting and deep cycle applications.

If you’ve seen new lithium power sport batteries, you have likely also seen that they come with higher cranking amps than the lead acid batteries they are replacing. You may even be concerned that the new higher cranking amps will be a problem for your application. Likewise, you may be worried about using a lithium battery with a higher capacity than what the lead acid had before it. Fear no more – a high cranking amp or high capacity battery will not damage your prized power sport vehicle – no matter if it is a cranking or deep cycle application!

Understanding How Amperage Works

To understand why, we need to dive into how the energy is transferred. You may have seen in our other blogs that electricity can be described using the analogy of water in a pipe.

The speed of the electricity is the amps, and the size of the pipe is the volts. These two characteristics make wattage, or the total amount of energy flowing through the pipe. A misconception is that the volts and amps ‘push’ their way to the device – this is where a concern arises that putting a 600 cranking amp lithium battery where a 450 cranking amp lead acid battery had been may cause damage.

Should I be worried about higher cranking amps in a lithium battery?

There is actually no valid concern here! The Ohm, your starter in this case, limits the flow of amps (this is also called resistance or impedance). Your starter is the same as it was with the lead acid battery, so the restriction it creates is unchanged. If you look to our blog about charging lithium batteries with an SLA charger, you can see that Power-Sonic has chosen the LiFePO4 chemistry for how similar its voltage is to charging and discharging a lead acid battery. If the Ohm and the Volt are the same, the Amp must also be the same! This means that even though your new lithium battery is capable of providing many more amps than a lead acid battery, the starter will only allow the amount of current it needs to flow.

Ultimately, there is no need for concern when your ‘drop-in replacement’ lithium power sport battery has a higher cranking amp or cold cranking amp rating than your current lead acid battery. In fact, it just means you will gain even longer life out of the battery when lithium already lasts longer than lead acid.

Over-sizing in deep cycle applications

Another common area where over sizing can bring you more energy for the size is in your RV battery system. A popular form factor lead acid deep cycle battery is Group 8D. These batteries will vary in capacity from 180 to 250 Amp hours and can weigh an astonishing 160 pounds!

The PSL-BTP-123000 is Group 8D, has Bluetooth communications to monitor the battery, only weighs 83 pounds, and packs in 300 Amp hours of lithium! As discussed before, there is no need for concern of a larger capacity battery damaging your RV’s electric system because your RV will only use as much power as it needs. This means your RV electronics will run longer with a lithium battery that fits in the same space as a weaker lead acid battery.

If over-sizing is ok, what about under-sizing?

Due to the high-performance nature of a lithium battery, under sizing the battery is highly discouraged and not recommended. Under-sizing a battery can potentially be very dangerous.

Again, using the illustration above, if the starter needs more amps (meaning it has lower restriction) than a lead acid battery is designed to support, the voltage in the lead acid battery will drop as there is a lack of restriction to the flow. This overload and voltage drop will simply shorten the life of the lead acid battery.

Conversely, a lithium battery will support very high discharge rates and if the starter provides little restriction, the battery will provide all its energy as fast as it can. This overwhelming amount of current in an under sized lithium battery generates a significant amount of heat in the lithium cells and can lead to severe damage and premature failure. Causing even further damage, after the engine starts, a lithium battery will accept a charge from the alternator far faster than a lead acid battery creating even more heat in the cells.

High levels of heat are the battery’s enemy – the larger the battery is, the less strain it will endure starting the engine, and not as much heat will be generated. For this reason, the more you are able to over size your battery, the longer it will last!

What about voltage?

An important word of caution about voltage. Over sizing only refers to capacity. If you use the wrong voltage (too high or too low) of battery in your application, significant damage will occur. Please always use the correct amount of voltage for your application as designated by the manufacturer.

Voltage in Marine Applications

Again, it is important to mind the voltage required by your application. You may use three Group 31 12V marine deep cycle batteries in series to make the 36V necessary to run your trolling motor. Most Group 31 lead acid batteries are rated at 80-100 Amp hours, but due to the high demand of a trolling motor they may only perform at 70 Amp hours or less. This means you could only be getting 75% of the runtime advertised from your lead acid battery!

Power Sonic’s group 31 lithium batteries can provide up to 125 Amp hours in the same group 31 case size while weighing nearly half as much. These lithium drop-in replacements will up to double the time you spend on the water without damaging your trolling motor (assuming proper series-connection).

Additionally, the constant power discharge of lithium not only allows you to get the full rated capacity out of the battery every cycle, but also generates a constant power output throughout the discharge. This stable power allows your trolling motor to hold your boat on station at any time during the discharge – no more drifting off station when the wind comes up and the battery is weak!

As you can see, lithium continues to be a very safe drop-in replacement option for lead acid in a multitude of applications. Please contact us if you have any questions or concerns regarding your lithium battery conversion.

Categories: Blog, Batteries, Lithium

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