I’ve been using the MillerTech 36V 105Ah Sun Up – Sun Down Sport Series Lithium Battery since it hit the market a few months ago, and I’ve been extremely impressed with it. After spending many days on the water, this battery has completely eliminated any anxiety I might have had with run time. The “Sun Up – Sun Down” name isn’t marketing hype; it has delivered all-day power with consistent performance from launch to retrieval. The voltage stays strong, there’s no noticeable drop-off throughout the day, and I never find myself watching the battery gauge.
The Bluetooth function is a welcome feature, and helped me realize I didn’t have to worry about capacity. Being able to monitor battery status, state of charge, and performance right from my phone provides great peace of mind while I’m on the water. The build quality is excellent, and the battery feels every bit like a premium product designed for serious anglers. Combined with the impressive capacity and 10-year warranty, it’s clear MillerTech built this battery to perform for years.
Installation On My Tracker Grizzly 1860 CC
One concern I had before taking delivery of the MillerTech 36V 105Ah Sun Up – Sun Down Sport Series was finding room for such a large battery in my Tracker Grizzly 1860 center console. The 105Ah model uses a larger Group 50 footprint (13.5″ L × 9.6″ W × 10.5″ H), so it’s definitely bigger than what many anglers are used to. I was pleasantly surprised that I was able to make it work. There was enough space to mount the battery under the center console as well as in the rear battery compartment area, giving me some flexibility with installation.
That said, because of the Group 50 dimensions, you’ll want to plan your layout carefully and purchase a battery tray specifically designed for the larger footprint. A standard marine battery tray likely won’t fit, so consider one of Millertech’s battery trays built specifically for their 36V 105AH and 12V 300AH batteries. Once I figured out the mounting location and secured it properly, the installation was straightforward.
Real-World Runtime
One of the best parts of this battery has been how much freedom it gives me on the water. My 8-year-old son absolutely loves running the trolling motor, and there are plenty of days when we spend more time cruising around than we do actually fishing. Sometimes he treats it like his own electric boat, and we’ll spend long stretches simply exploring different parts of the lake. Those family adventures can put more demand on a trolling motor battery than a typical fishing trip, with our Minn Kota Fortrex getting a serious workout.
Many of our trips are on a smaller local lake where it simply doesn’t make sense to fire up the 90 HP outboard. Instead, we’ll launch the boat and spend the entire day running exclusively on the trolling motor. We move from shoreline to shoreline, work weed edges, check out coves, and sometimes just cruise around enjoying the day. The trolling motor is constantly in use, often at higher power settings, and the battery handles it effortlessly.
What has impressed me most is that even after a full day of using the Fortrex as our primary means of propulsion, I still have plenty of battery capacity remaining. There have been several trips where we launched in the morning, spent hours fishing and exploring, and returned to the ramp in the evening without even dipping below ¾ capacity. That’s a huge change from my previous setup, where battery status was always somewhere in the back of my mind.
| Specification | Details |
| Chemistry | LiFePO4 (LFP) |
| Capacity | 105Ah |
| Weight | 68.2 lbs |
| Dimensions | 13.5″ L × 9.6″ W × 10.5″ H |
| Max Charge Voltage | 43.2V |
| Peak Discharge Current | 300A (5 seconds) |
| Continuous Discharge Current | 150A |
| Max Charge/Discharge Current | 100A |
| Low Cut-Off Voltage | 30V |
| Operating Temperature | -4°F to 140°F |
Fast and Convenient Charging
I’ve paired the battery with MillerTech’s 36V 15A On-Board Lithium Battery Charger, and the combination has been outstanding. The charger delivers 43.5V at 15A and is specifically designed for 36-volt LiFePO4 batteries, making it a perfect match for the 105Ah Sport Series battery. It’s IP65 waterproof-rated and designed for permanent mounting in a boat, though I use it as a portable unit because I also utilize it to top off my other 36-volt batteries.
With over 4,000Wh of capacity available in the battery, I expected recharge times to be much longer. Instead, the 15A charger does an excellent job replenishing the battery overnight after even the most demanding days on the water. Between the charger and the battery’s built-in Bluetooth monitoring, it’s easy to check charging progress and know exactly where the battery stands before the next trip.
Final Thoughts
After months of real-world use, I can confidently say that the MillerTech 36V 105Ah Sun Up – Sun Down Sport Series Lithium battery has lived up to its name. The combination of exceptional runtime, reliable power delivery, Bluetooth monitoring, and fast charging has completely changed the way I think about powering a trolling motor.
While the larger Group 50 footprint does require a little extra planning during installation, I view that as a worthwhile tradeoff. Instead of finding room for multiple batteries, dealing with additional wiring, and managing a more complicated setup, I have a single battery that delivers all the power I need for a full day on the water. The slightly larger size is more than offset by the simplicity and convenience of having one high-capacity battery handling the job.
For anglers who spend long days on the water, families who enjoy cruising with an electric motor, or anyone looking to maximize runtime while minimizing complexity, the MillerTech 36V 105Ah Sport Series is an excellent choice. It’s easily one of the best upgrades I’ve made to my Tracker Grizzly 1860 CC.
