Search results for "VRLA vs AGM" are a small monument to a confusion the industry profits from and buyers pay for. VRLA — valve regulated lead acid — is the family name for sealed lead acid batteries whose gases recombine internally and whose case opens only through a pressure-relief valve. AGM is one construction inside that family. Gel is the other. Every AGM battery is a VRLA battery; not every VRLA battery is AGM. This article untangles the terms, because the confusion is not academic: it writes wrong specifications into tenders, and wrong batteries into cabinets. Our own VRLA page presents the family; the gel pages present the other branch.
The family tree
- Lead acid — the chemistry.
- Flooded (vented) — free liquid electrolyte, open or vented caps, the OPzS discipline: serviceable, attended.
- VRLA (sealed, valve regulated) — immobilised electrolyte, recombinant, maintenance free.
- Inside VRLA: AGM — electrolyte absorbed in glass mat.
- Inside VRLA: Gel — electrolyte gelled with silica.
"SLA" (sealed lead acid) is simply VRLA’s trade nickname — the term our sealed lead acid page uses because buyers search for it. Three labels, one family, two branches. Once the tree is clear, most specification muddles dissolve: a tender asking for "VRLA, AGM type" is coherent; one asking a supplier to choose "between VRLA and AGM" has not yet asked a question.
Why the branches still matter
Correcting the category error should not collapse the real distinction beneath it. AGM and gel behave differently where it counts — AGM’s low internal resistance serves high-rate standby; gel’s immobilised electrolyte serves deep cycling and heat — and they charge at different voltages. The full duty-by-duty comparison lives in our gel vs AGM guide. The terminology point is about where the decision sits: first choose sealed (VRLA) versus flooded — a maintenance and siting decision. Then, inside sealed, choose the branch — a duty decision. Skipping the first question is how flooded batteries end up specified for unmanned cabinets, and skipping the second is how gel ends up on flooded charger settings.
Reading supplier language critically
Three phrases deserve a buyer’s raised eyebrow. "VRLA battery" with no branch stated: ask which — the price difference between branches is real, and an unstated branch is usually the cheaper one. "AGM gel battery": a hedge that names both branches to catch both searches; a physical battery is one construction — our own range’s hybrid-designated model is documented as such precisely because the designation is unusual, and we say so on its page. "Maintenance-free VRLA": redundant but harmless — maintenance-free is what VRLA means. Precision in the small words predicts precision in the large ones; buy from datasheets that name the branch, the rating rate and the warranty in the same breath.
So is a gel battery a VRLA battery?
Yes — gel is the second branch of the VRLA family, alongside AGM.
Is SLA different from VRLA?
No. SLA (sealed lead acid) is the common trade name for the same valve-regulated family.
Three tender sentences, corrected
Tender documents are where the VRLA/AGM confusion does its expensive damage, so here are the corrections in the form buyers can paste. Wrong: "Battery shall be VRLA or AGM type." Corrected: "Battery shall be valve-regulated lead acid (VRLA), AGM type" — or gel type, as the duty decides; the sentence must name the branch. Wrong: "Maintenance-free AGM gel battery." Corrected: name one construction; a battery is built one way, and the charger profile will be set to match it. Wrong: "Sealed lead acid, 100Ah" with nothing else. Corrected: add the rate basis of the capacity, the branch, and the warranty term — the three facts without which two compliant bids can be different batteries. None of this is pedantry: each correction removes a documented way that compliant paperwork delivers the wrong product.
And a closing symmetry worth remembering: the same discipline applies at the other end of the market. A buyer who writes precise tenders receives precise batteries; a factory that publishes precise datasheets — branch, rate, weight, dimensions, warranty on one page — is telling you how it will behave when something goes wrong. Judge both by the small words.
Is "SLA battery" acceptable in a tender?
It is understood everywhere, but VRLA plus the branch name is the precise form. Use SLA in conversation; write VRLA (AGM) or VRLA (gel) in documents that money follows.
A two-minute terminology audit for your own documents
Take any battery document your organisation issued in the last year — a tender, a purchase order, a maintenance contract — and audit it with this guide. Find every occurrence of "VRLA" standing alone where a construction was meant: flag. Find "gel" and "AGM" in the same product phrase: flag. Find a capacity with no rate basis: flag. Find "maintenance free" used as a construction: flag. Most organisations complete the audit in minutes and find two or three flags, each a place where a supplier could — in good faith or otherwise — deliver something other than what operations expected. The audit’s value is not embarrassment; it is that the next document goes out clean, and clean documents are the cheapest quality programme in the battery business. Suppliers read your documents the way you read their datasheets: as evidence of how the relationship will behave when a number is disputed.
Why the words will keep mattering
Battery vocabulary is not converging on its own: marketing prefers fog, new entrants inherit the fog, and every year’s tender templates copy last year’s. The correction therefore belongs to the buyers and specifiers, document by document — parent term, branch name, rate basis, warranty — because those documents are where money changes hands on the strength of words. The good news is that precision is cheap and contagious: one clean tender teaches every bidder who reads it, and a supplier who answers precision with precision has told you the most important thing about themselves before a single battery ships. Start with the audit in this guide, on your most recent document. It takes two minutes, and it is the highest-yield two minutes in battery procurement.
One last usage note for the maintenance log: record the branch, not just the family, at every service entry. "VRLA replaced" tells the next technician nothing about what profile the charger should hold; "VRLA (gel) replaced, profile confirmed" tells them everything. Small words, again — the whole guide in one log line.
Precision, in the end, is a form of respect — for the technician who will service the battery, the auditor who will read the file, and the buyer whose money follows the words.
Write the branch name. Every time. It costs four characters and saves entire replacements.