Lithium Boat Battery Upgrade: Charge Your Trolling Motor While You Run
What if your trolling motor batteries charged themselves every time you ran down the lake?
That’s the setup one customer drove home with. He stopped in at our shop with his boat and everything he needed. He just wanted a lithium boat battery upgrade: lead-acid out, MillerTech lithium in. Here’s what we did and why it works so well.
Five Lead-Acid Batteries Out, Four Lithium Batteries In
We pulled five Interstate lead-acid batteries out of his boat and replaced them with four MillerTech Sport Series lithium batteries and one smart charger:
- Two 12V 135Ah Sport Series Dual Purpose batteries to crank the outboard. Each one delivers 1,500 cold cranking amps (CCA) in a Group 31 case and weighs 33 lb.
- Two 36V 60Ah Sport Series trolling motor batteries to run the trolling motor. One of these does the job of three Group 27 lead-acid batteries.
- One Dark Speed “On The Run” 12V/36V charger to keep both banks charged, at the dock and on the water.
Fewer batteries means fewer connections to wire and fewer things to check.
How the Dark Speed Charger Keeps Everything Full
The Dark Speed is a dual-bank charger, so one charger handles both his 12V cranking batteries and his 36V trolling motor batteries.
At home: plug it into a regular outlet and it charges both banks at the same time.
On the water: this is where it gets good.
- While the outboard runs, its alternator charges the 12V cranking batteries first.
- Once those are full, the Dark Speed sends the extra power to the 36V trolling motor batteries.
- You keep fishing on batteries that were topping off during every run across the lake.
His outboard has a big 80A alternator, so it fills the cranking batteries fast and has plenty left over for the trolling motor. “With this setup, there’s a good chance he might never have to plug these batteries into an AC outlet,” our tech said.
No daily shore power, no generator, and no cutting your day short because the trolling motor is running low.
Why Switch From Lead-Acid to Lithium
- It lasts years longer. MillerTech lithium iron phosphate (LiFePO4) batteries are rated for more than 3,000 cycles and about 10 years. Lead-acid typically gets 150 to 300 cycles and lasts one to two years.
- You get the power you paid for. Lithium delivers 99% of its rated capacity. Lead-acid gives you 50% to 60%.
- No maintenance. No watering and no acid.
- You can see what’s left. Every Sport Series battery has Bluetooth, so the MillerTech app shows capacity, voltage, and temperature on your phone. With your permission, our team can also log in through the app and help fix a problem remotely.
- It’s backed for 10 years. Sport Series batteries carry a 10-year warranty. If one fails, we repair or replace it and pay shipping both ways. The warranty even transfers if you sell the boat.
- Cold-weather option. Fish late in the season? The 12V 135Ah and 36V 60Ah both come in heated models that can charge below freezing.
Ready to Upgrade Your Boat
Stop in at the shop and we’ll swap your batteries for you. Or order online at millertechenergy.com and we’ll ship them to you. Most orders arrive in two to three days.
Not sure which batteries or charger fit your boat? Call 855-MAX-LITH (855-629-5484) and a real person who knows the products will help you build your setup. You can also email [email protected].