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A cabin light that stays on through the night and a trolling motor that pushes a boat across the lake ask the same thing of a battery: steady power for a long time. The battery that does that job is a deep cycle battery, and what is deep cycle is the question this guide answers. It explains what a deep cycle battery is, how it differs from a starter battery, and where it is used, with figures from battery listings.
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The quick answer
A deep cycle battery is a battery built to be drained and recharged again and again. A starter battery gives a short burst of power to crank an engine, while a deep cycle battery gives steady power over a long time. The Mighty Max listing states a 12V 35Ah sealed lead acid battery listed as a deep cycle AGM solar battery, which is the kind of battery this guide describes.
Step 1: What is deep cycle
Deep cycle describes how a battery is used, not how it looks. A deep cycle battery is drained down and recharged as part of its normal work, and the Mighty Max listing states its battery has a characteristic of deep discharge recovery. The same listing states a high discharge rate, a wide temperature range and a long service life. A battery built for that job is made to give its power slowly and to take a full recharge after.
| Reference battery | Size | Type | Role |
|---|---|---|---|
| Mighty Max ML35-12 | 12V 35Ah | SLA AGM | Deep cycle solar battery |
| Milwaukee M18 REDLITHIUM FORGE HD12.0 | M18 tool pack | REDLITHIUM | Tool battery, not deep cycle |
The listing states the battery is a 12V 35Ah sealed lead acid battery, maintenance free. Amp-hours state how much charge the battery holds: 35Ah is the figure for this battery, and the listing states it replaces 33Ah, 34Ah and 36Ah batteries. Voltage states the system it fits: 12V is the figure for this battery, and it is the voltage the loads and the charger have to match.
Step 2: Compare it with a starter battery
A starter battery and a deep cycle battery do different jobs, and the diagram of each system shows it. A starter battery gives a short burst to crank an engine, then the engine keeps it near full charge. A deep cycle battery gives steady power for hours, drains down, and is recharged after. Starter and deep cycle batteries look alike from the outside, but they are built for different work, and swapping them is the wrong call.
Batteries are also built for different tools. A Milwaukee listing states an M18 REDLITHIUM FORGE HD12.0 battery pack for power tools, with overload protection and an onboard fuel gauge. That pack is a tool battery, not a deep cycle battery, and it shows the point: a battery’s build follows its job, and the job of a deep cycle battery is steady power over a long time.
Step 3: Look at the types
Deep cycle batteries come in several types, and the type states how the battery is built. The Mighty Max listing states a sealed lead acid battery, AGM, maintenance free. Sealed lead acid batteries hold their acid in place, AGM holds it in glass mat, and each is a type of lead acid battery. See the battery types guide for how the types compare.
Lithium is the other type the listings name. A Milwaukee listing names its pack REDLITHIUM, and the pack is built for power tools, with a housing resistant to common oils, greases and solvents. The listings here do not state a lithium deep cycle battery, so this guide does not describe one. The type to pick is the one the loads and the charger are built for.
Step 4: Check where it is used
Deep cycle batteries sit in the systems that drain them slowly: solar setups, trolling motors, power chairs and golf caddies. The Mighty Max listing states compatibility with a deep cycle AGM solar battery, and names trolling motors, a solar generator, a power chair and a golf caddy among its uses. The listing also names tractors, riding mowers, kayaks and utility vehicles, which shows how wide the uses run.
Check the listing’s compatibility before buying: the Mighty Max listing states it replaces 33Ah, 34Ah and 36Ah batteries, so a battery of that size fits the systems the listing names. The dimensions have to fit too: the listing states different figures in the bullets and the spec table, so measure the space and trust the bullets where the figures disagree. See the deep cycle battery sizes guide for how group size works.
Ways to choose a deep cycle battery
- Match the voltage: the Mighty Max listing states 12V, and the loads and the charger have to match it.
- Match the capacity: the listing states 35Ah, and it replaces 33Ah, 34Ah and 36Ah batteries.
- Check the type: sealed lead acid AGM, maintenance free, with deep discharge recovery stated in the listing.
- Check the dimensions: the listing states different figures in the bullets and the spec table, so measure the space and trust the bullets where the figures disagree.
FAQ: power away from the grid
What is a deep cycle battery?
A battery built to be drained and recharged again and again, giving steady power over a long time. The Mighty Max listing states a 12V 35Ah sealed lead acid battery listed as a deep cycle AGM solar battery.
What is the difference between a deep cycle battery and a starter battery?
A starter battery gives a short burst to crank an engine, while a deep cycle battery gives steady power for hours. A starter battery is built to stay near full charge, while a deep cycle battery is built to drain down and recharge.
Can a deep cycle battery start a car?
It is the wrong tool for the job. A deep cycle battery is built for steady power, not the short burst a starter needs. Use the battery the vehicle manual names for starting, and a deep cycle battery for the loads that drain it slowly.
How long does a deep cycle battery last?
It depends on how deep it is drained and how often it is recharged. The Mighty Max listing states a long service life and deep discharge recovery, and a sealed lead acid battery that is kept charged lasts longer than a battery left flat.
Related solar guides
See the battery types guide, the deep cycle battery sizes guide, the deep cycle battery maintenance guide, the LiFePO4 battery vs deep cycle battery guide and the batteries guides.
