Lead Acid Battery: Types, How It Works and Which to Buy
A lead acid battery stores energy in lead plates sitting in dilute sulphuric acid, and it is still the most common battery for UPS, solar and vehicles in Pakistan. It comes in several types: flooded (the "acid" or liquid battery), tall tubular, sealed SMF and VRLA, AGM and gel. This guide explains how a lead acid battery works, the difference between a cell and a battery, each type in plain words, and which one suits your use.
Updated 12 November 2026
What is a battery, and what is a cell?
A cell is a single unit that turns chemical energy into electricity. In a lead acid battery each cell makes about 2 volts. A battery is a group of cells joined together. A 12V lead acid battery is six cells in series inside one box; a 24V block is twelve. So "what is the difference between a cell and a battery?" has a simple answer: a battery is made of cells. Large banks sometimes use single 2V cells, such as the Narada EoSG gel cells, joined outside in rows.
How a lead acid battery works
Each cell has positive plates of lead dioxide and negative plates of spongy lead, separated by thin insulating sheets and soaked in an electrolyte of dilute sulphuric acid. When the battery gives power, both plates slowly turn into lead sulphate and the acid gets weaker. When you charge it, the process runs backwards. If a battery is left flat for long, the lead sulphate hardens into crystals that will not turn back. That is called sulphation, and it is the main reason lead acid batteries lose capacity. Charging promptly and fully is the best protection.
Flooded (wet or acid) batteries
A flooded battery has free liquid acid and removable caps or float indicators. Pakistanis call it an acid battery, liquid battery or wet battery. It loses a little water while charging, so you top up with distilled water. Flooded batteries are cheaper, tolerate some over-charging and are easy to check with a hydrometer. Examples: Exide HP, Phoenix UGS and UGLT, Osaka HT-IPS, Daewoo DSS and all tall tubular batteries. "Dry charged" flooded batteries, such as Volta's IPS series, leave the factory without acid and are filled before first use; they are still flooded batteries.
Tubular vs flat plate
Inside a flooded battery the positive plate can be a flat grid pasted with lead oxide (flat plate) or a row of tubes filled with active material (tubular). Tubes hold the material in place during deep discharge, so a tubular battery survives daily deep cycling far longer. Flat-plate batteries are cheaper and give strong bursts of current, which suits cars and short UPS cuts. "Tubular battery vs lead acid battery" is a common search, but a tubular battery is a lead acid battery, just built differently. See tubular batteries (Tubular Battery) and UPS batteries (UPS Battery).
Sealed batteries: SMF, VRLA, AGM and gel
- SMF (sealed maintenance free): a sealed battery you never top up. Pakistanis call it a dry battery.
- VRLA (valve regulated lead acid): the technical name for sealed lead acid batteries. A one-way valve lets out excess gas, and the gas mostly recombines inside, so no water is lost. Example: Phoenix VR12-200.
- AGM (absorbent glass mat): the acid is soaked into glass-fibre mats. Most dry UPS batteries and start-stop car batteries such as the Varta F21 Silver Dynamic AGM are AGM.
- Gel: the acid is thickened into a gel with silica. Gel handles deep cycling and heat a little better than AGM. Examples: Narada MPG12V200 and Long WPG200.
All sealed types need the correct, slightly lower charging voltage. See dry batteries (Dry Battery) and gel batteries (Gel Battery).
Which battery is better, dry or acid?
For a home UPS with long daily cuts, a flooded tall tubular usually gives the most years per rupee, as long as you add water. A dry (sealed) battery costs more but needs no water and gives off almost no fumes, so it suits flats, bedrooms and offices. For cars, both work; sealed maintenance-free batteries save effort. For daily solar cycling, tubular, gel or lithium are the strong choices. Our dry vs tubular guide (Dry vs Tubular Battery: Which One Should You Buy?) goes deeper.
Deep cycle vs starting batteries
A deep cycle battery is built to be drained and recharged again and again, like a UPS or solar battery. A starting battery (car, truck or generator) is built to give a big current for a few seconds and is then kept full by the alternator. Using a starting battery on a UPS wears it out fast. See deep cycle batteries (Deep Cycle Battery).
Lead acid price compared with lithium
A lead acid battery is cheaper on day one and easy to replace anywhere. A lithium (LiFePO4) battery costs more but gives about 90% of its capacity, against about 50% for lead acid, and lasts several times as many cycles. For a battery that cycles every day, lithium often costs less over its life. Compare in our lithium vs tubular guide (Lithium vs Tubular Battery: Which Is Better for Solar?).
