Specification · Battery types
AGM vs EFB vs Flooded Batteries Explained
Three constructions cover almost every car and van on UK roads. Conventional flooded batteries suit older vehicles without stop-start. EFB (Enhanced Flooded Battery) is a strengthened flooded design built for entry-level stop-start. AGM (Absorbent Glass Mat) holds its electrolyte in a glass fibre mat, tolerates deep cycling far better and is specified on higher-demand stop-start and premium vehicles.
The rule that matters in practice: you can normally move up the list, never down. An AGM car must not receive an EFB or flooded battery; an EFB car must not receive a plain flooded one. Going the wrong way does not usually break the vehicle — it destroys the battery early, and the owner blames the brand rather than the specification.
Key points at a glance
- Flooded
- Standard construction, non stop-start vehicles
- EFB
- Reinforced flooded, entry-level stop-start
- AGM
- Glass mat, heavy stop-start and high electrical load
- Substitution rule
- Upgrade is usually fine, downgrade is not
What this means in practice
- AGM handles repeated partial discharge, which is exactly what stop-start traffic does to a battery all day.
- EFB is a genuine engineering step above flooded, not a marketing label — plate design and separators differ.
- Charging profiles differ, which is one reason vehicles want a new battery registered to them.
- AGM is sealed and cannot be topped up, so heat-driven water loss is permanent.
- Physical case size, terminal layout and hold-down type must match too — the right chemistry in the wrong case is still the wrong battery.
Questions we get asked
Can I fit AGM to a car that came with flooded?
Usually yes, provided the case size and terminals match. It is an upgrade in cycling ability, though on a simple vehicle without stop-start you may not see the full benefit.
How do I know which one my car needs?
The existing battery is usually labelled, and the vehicle's specification confirms it. We check both before fitting rather than relying on the label alone, because the previous battery may itself have been wrong.
Is AGM always the better choice?
Not always — it is the right choice where it is specified. On a vehicle designed for flooded, the extra cost may buy you durability you never use.
Not sure which type your vehicle takes?
We identify the correct specification on site and fit it properly, including coding where needed.
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