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A dead alarm battery and a solar bank that runs dry share the same question: which lead-acid type fits the job. Lead acid battery types split into flooded, AGM and gel under the sealed VRLA umbrella, with deep-cycle and starting builds for different loads. This guide explains each type, what makes it different, and how to match it to the job.
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The quick answer
All lead-acid batteries store energy in lead plates and acid, but the types differ in how the acid is held and what the battery is built to do. Flooded batteries hold liquid acid and need water added; AGM batteries hold the acid in glass mats and are sealed; gel batteries hold it in a gel. The listings cited here are all sealed AGM types: a Miady 12V 5Ah battery (on Amazon), an Energizer 12V 7Ah battery and a Mighty Max 12V 35Ah battery. Deep-cycle types give steady energy over time for solar storage and backup, while starting types give short bursts for engines. See the lead acid battery types guides for the category.
The table below lines up the main types.
| Type | Acid held | Maintenance |
|---|---|---|
| Flooded | Liquid acid in open cells | Water added as needed |
| AGM | Acid absorbed in glass mats | Maintenance-free |
| Gel | Acid held in a gel | Maintenance-free |
The Miady, Energizer and Mighty Max listings cited here are all sealed AGM batteries, in 5Ah, 7Ah and 35Ah sizes.
Flooded lead-acid batteries
A flooded battery holds liquid acid in open cells with caps, and gas escapes through vents as it charges. Water must be added as the level drops, and the battery must stay upright so acid does not spill. Flooded batteries are the oldest lead-acid type and the usual choice for engine starting, where short bursts of high current matter. None of the listings cited here is a flooded battery: the Miady, Energizer and Mighty Max listings are all sealed types.
AGM batteries
An AGM battery holds the acid in glass mats pressed between the plates, so there is no liquid to spill and no water to add. The Miady listing says its battery uses AGM technology with a wide temperature range and an ABS plastic case that resists shock, vibration and heat. The Energizer listing says its AGM design gives efficient gas recombination and virtually eliminates maintenance, with a valve-regulated, spill-proof design and overpressure venting. AGM batteries recover from deep discharge: the Miady and Mighty Max listings note deep discharge recovery and a high discharge rate. The Miady battery is 12V 5Ah, the Energizer battery (on Amazon) is 12V 7Ah, and the Mighty Max battery is 12V 35Ah, so the same AGM build covers small alarm batteries and larger solar storage. The Energizer listing notes its battery is usable in any position except upside down, while the Miady listing says its battery can be mounted in any position.
Gel batteries
A gel battery holds the acid in a silica gel, so it is sealed and maintenance-free like AGM. Gel batteries suit steady, low-current loads and tolerate deep discharge. No listing cited here is a gel battery, so compare gel and AGM figures in the listings before choosing between them. See gel vs flooded batteries for solar for how gel compares with flooded types.
Deep-cycle and starting batteries
A deep-cycle battery is built to give steady energy over a long discharge and to recover from it, while a starting battery is built to give a short burst for an engine. The Mighty Max listing calls its battery a deep cycle AGM solar battery, and the Miady listing warns that its battery is an energy storage battery, not a power battery. The Miady battery is rated at a 20-hour rate, which is the steady-discharge measure for storage batteries. Use a deep-cycle battery for solar storage, backup power and alarm systems, and a starting battery for engine cranking. The Energizer listing names home alarm systems, backup power, scooters, garage and gate openers, UPS backup units and emergency lighting among its uses.
Lead acid battery types: how to choose
Choosing comes down to the acid, the use and the maintenance you accept. Work through the checks below before you buy.
- Type: check whether the listing names flooded, AGM or gel, and whether it is sealed or vented.
- Voltage and capacity: check the voltage and the amp-hours: 12V in the listings cited here, in 5Ah, 7Ah and 35Ah sizes.
- Use: check the use the listing names: deep-cycle for solar storage and backup, and starting for engine cranking.
- Maintenance: check whether the battery needs water added: AGM and gel are maintenance-free, while flooded needs water.
- Mounting: check the mounting the listing allows: the Miady battery mounts in any position, and the Energizer battery mounts in any position except upside down.
- Warranty: check whether the listing states a warranty term: 12 months for the Miady battery, and 2 years for the Energizer battery.
FAQ: power away from the grid
What is the difference between AGM and flooded batteries?
An AGM battery holds acid in glass mats and is sealed and maintenance-free, while a flooded battery holds liquid acid and needs water added. The Miady and Energizer listings describe AGM batteries with no water adding, and the Energizer listing says its AGM design virtually eliminates maintenance.
Are sealed lead-acid batteries maintenance-free?
The listings cited here say so: the Miady battery is maintenance-free and spill proof through VRLA technology, and the Energizer AGM battery virtually eliminates maintenance with gas recombination. A sealed battery still needs the right charger and the right voltage.
Can an AGM battery be mounted on its side?
The Miady listing says its battery can be mounted in any position, and the Energizer listing says its battery is usable in any position except upside down. Check the listing for the battery you buy, since mounting limits differ by model.
What does the 20-hour rate mean for a 5Ah battery?
The Miady 12V 5Ah battery is listed as a 20-hour battery, which means its 5Ah capacity is rated over a 20-hour discharge. Capacity is rated over the stated hours, so a faster draw gives less than the listed capacity.
How long does a sealed lead-acid battery last?
Check the warranty the listing states: 12 months for the Miady battery, and 2 years for the Energizer battery. How long a battery lasts depends on how it is used and charged. See how long a lead acid battery lasts for what affects battery life.
Related solar guides
See the Batteries and Charging guides, the lead acid battery maintenance guide, the best deep cycle batteries for a refrigerator and the deep cycle battery maintenance tips.
