I’m sure you’ll get longer run time out of the new battery, but those battery percentage numbers are going to be inaccurate and irrelevant. Your Helix is reading the battery voltage and showing a corresponding capacity percentage remaining. The percentage is based off of lead acid batteries with 13.7v at full charge. The LiFePO4 battery has 14.6v at full charge.
Battery indicators for all flasher/fish finders using the LiFePO4 batteries won’t be accurate. However, there should be screen on your helix that shows battery voltage and you can monitor that to have an idea when your battery is getting low. The energized outdoors 10ah battery will shut down at 10.0v, and I’m not sure if the Helix will shut off before it gets to that.