All of it. A Millertech LiFePO4 battery delivers 100% of its rated capacity, compared with 50% to 60% from lead-acid. A 100Ah lithium battery gives you roughly the usable power of two 100Ah lead-acid batteries.

The numbers add up quickly:
• A 12-inch graph pulls about 2–3A.
• Forward-facing sonar adds 3–5A.
• With lighting and device charging, a full setup typically runs 6–8A.
Millertech’s 12V 135Ah and 190Ah Dual Purpose batteries are rated to run multiple power-hungry graphs for 8+ hours.

Roughly half or more. One 36V 60Ah Sport Series battery (3660-BT) weighs 41.23 lb and replaces three Group 27 lead-acid batteries. Millertech says that cuts more than 50% of the weight. For 12V, a Millertech 100Ah AGM weighs 70 lb, while the 12V 100Ah Dual Purpose lithium weighs 31 lb.

Keep the battery plugged into the charger whenever it’s not in use. For long-term storage (1 month or more), fully charge the battery, remove all loads, and store it with nothing connected. Following these steps will help maximize the lifespan of your lithium deep cycle battery.

For long-term storage, fully charge the battery, remove all loads or connections, and store it with nothing attached. This preparation helps maximize the battery’s lifespan during extended storage periods, such as over the winter.

It’s still worth a look, but for different reasons. If you’re always plugged in, you won’t feel the extra run time much. You will notice the weight: our 12V 100Ah weighs 26.55 lb, about a third of a 100Ah AGM. You’ll also skip the water checks and corroded terminals, and you won’t be replacing batteries every few seasons. If you’re starting to think about dry camping, lithium is where it really pays off.

Yes, once you look at cost per cycle and not just the price tag. A Millertech LiFePO4 battery is rated for more than 3,000 cycles, compared with 600–800 for an AGM. It can also last up to 10 times longer than sealed lead-acid. Add the 10-year Sport Series warranty and it costs less over the life of your boat.

No. Phones and laptops use lithium-ion cells built to pack the most power into the least space. Millertech RV batteries use lithium iron phosphate (LiFePO4), which is widely recognized as one of the most stable lithium chemistries. It gives off no gas while charging, and our batteries are UL certified to UL 1973. (Myths blog; UL certified page)

1Ah equals 1,000mAh, so the Max 8.0 is a 28,000mAh battery and the Max 4.0 is a 14,000mAh battery. Watt-hours (Wh) are the fairest way to compare packs at different voltages: the Max 8.0 stores 310Wh and the Max 4.0 stores 155Wh.

We lean toward one 36V battery, mostly for reliability. When three 12V batteries run in series, every one of them has to work perfectly, because if one fails, the whole system goes down. That gives you three times the chance of a failure compared with a single 36V battery. One weak battery also drags the others down: if one of three 12V 100Ah batteries only delivers 75Ah, the whole bank drops to 75% capacity.

Want a backup on the water?

Yes, we recommend charging the battery right away when you receive it. Due to shipping restrictions, batteries are not shipped fully charged, so an initial charge is necessary.

During your active season, yes. Keep the battery on the charger whenever you’re not using it. The BMS and the charger’s own cut-off together mean it can’t be overcharged. For storage of a month or more, follow the instructions on this video:
How to Winterize Your Boat's MillerTech Batteries