The short answer to this questions is no. Voltage does play a huge role in image quality, but voltage higher than 12.5v do not give you better image quality. First, we will explain why some people think it will give you better image quality and then we will describe what you can do to get the best image on your forward facing sonar units.
The number one reason people claim they get better image quality on higher voltage is due to them switching their batteries from a lead acid power source to a Lithium Battery isolating electrical interference. It does not matter if you are running 12.8V LiFePO4 or a higher voltage battery. Lead acid batteries will start at 12.8V, and not long after running your electronics, your voltage can drop below 12v. This is what typically causes image quality issues. Also, running your FFS on a starting battery introduces electrical interference.
The second reason people claim they get better image quality on higher voltage batteries comes down to them believing what some lithium batteries are advertising and telling them. This really causes confusion. There are lithium battery companies that claim higher voltage gives them better image quality. They may also sell products that will take your 24v-36V batteries and convert votlage to 16-24v. These are gimmicks and not the best solution. These are opportunities for them to market and sell you something. They are trying to create demand.
A 12.8V LiFePO4 battery will discharge between 12.8-13v for almost the full duration of the battery capacity (with Amped Outdoors Products). We have side by side tested these against 14.8V NMC batteries, 16V LiFePO4 batteries and even 24v batteries. The image quality stayed the same in all side by side tests. This also also been tested by most FFS manufacturers and other reputable rigging companies with similar results. Another fact proving this is when using our 14.8V NMC battery, the voltage starts at 16.8V and while in use will slowly lose voltage until it reaches 12V and shuts down fully depleted. If higher voltage meant better image quality, then you would see a reduction in image quality as you use the product. No one has ever reported this and we have not been able to see it in your tests. Fishing electronics draw a specific amount of power measured in Watts. Higher voltage batteries only mean you draw less amps. The only time we have seen higher voltage being an advantage is if someone is using inadequate wire size, where they experience voltage loss over the wire run.
Here is what you can do to get the best image quality with FFS
1) Dedicated your electronics to a lithium battery - This will eliminate electrical interference from other 12V components in your system. It will also keep your electronics running above 12.5V throughout the day.
2) Proper Installation - There are many companies selling wiring for fishing electronics. You can use these or run proper gauge wiring for your electronics to avoid voltage loss. Typically 10awg wiring run to each of your electronics will prevent voltage loss in your system. It is also important to use the proper marine wiring, connections and a good crimping tool. Loose and corroded connections are huge factors for causing problems.
3) Proper settings on your electronics - Straight of the box settings are a great starting point, but not going to be ideal. There are many videos on the internet on how to baseline setup your FFS units. I would find one to fit your needs and use that as a baseline. Understand what settings can do for you and this will allow you to make on the fly adjustments based on the waters you are fishing.
Why we sell higher voltage batteries? - We sell higher voltage products, specifically 14.8V NMC batteries. Our NMC batteries were developed for portable anglers who want the most capacity, in the smallest form factor, with the lowest weight. NMC cells have higher energy density, allow us to create this type of product. With NMC cells, you can get 11.1V or 14.8V. 11.1V batteries are obviously too low of voltage for fishing electronics which is why we were the first to release the 14.8V version. The working voltage is 16.8V and discharge to about 12V for full capacity, which is really good working voltage range. Our 12.8V LiFePO4, will give the same performance, but discharge around 12.8-13V for the full duration of the battery life. Much different than NMC as LiFePO4 will be heavier and larger. LiFePO4 are always going to be recommend for on board boat use.