This manual covers the safe installation, charging, operation, maintenance, and storage of ATB Power sealed valve-regulated lead-acid (VRLA) batteries in both AGM and GEL constructions. Read it in full before installing or charging any battery.
AGM: GP (General Purpose), DC (Deep Cycle), FT (Front Terminal), HR (High-Rate), LC (Long-Life Cyclic), 2V Long-Life Cells, Lead-Carbon (LDC), and Start-Stop (SSL) series.
GEL: Gel 12V cycling and Gel 2V standby series.
Lead-acid batteries store large amounts of energy and contain corrosive sulfuric acid electrolyte. Servicing must be performed only by trained personnel who have read and understood this manual. Keep this manual with the equipment.
Do not open, drill, crush, incinerate, or disassemble the battery. Do not attempt to add water — VRLA batteries are sealed and maintenance-free. Do not charge a frozen battery. Do not install or charge in a sealed, unventilated enclosure.
ATB VRLA batteries are sealed, valve-regulated lead-acid batteries. The electrolyte is immobilized, so the battery is non-spillable and can be operated in any orientation except continuously inverted. A one-way pressure-relief valve releases gas only if internal pressure rises abnormally; under normal float and cyclic charging the oxygen-recombination cycle returns gas to water inside the cell, so no water addition is required.
In an Absorbent Glass Mat (AGM) battery the electrolyte is held in a fine glass-fibre separator between the plates. AGM offers low internal resistance, high discharge rates, fast charge acceptance, and strong performance in standby, high-rate, and cyclic duty.
In a GEL battery the electrolyte is immobilized as a thixotropic gel by adding fumed silica. GEL excels in deep-cycle and high-temperature service, offers excellent cycle life at deep depth-of-discharge, and tolerates partial-state-of-charge use well. GEL requires a lower charging voltage than AGM (see Section 5).
AGM and GEL are both VRLA and share most handling, installation, and safety rules. The main practical difference is the charge voltage setting. Always select the charger profile (AGM or GEL) that matches the battery installed.
Store batteries indoors in a clean, cool, dry place, upright, away from direct heat and sunlight. VRLA batteries self-discharge slowly — typically 1–3% per month at 25°C (77°F). Lower temperatures slow self-discharge; higher temperatures speed it up.
Storing VRLA batteries in a deeply discharged state, or for too long without a refresh charge, is a common cause of premature failure and permanent capacity loss.
Correct installation is the first step to getting full life and performance from the battery.
Clean terminals and connect the load and charger with the correct hardware. Make the final positive connection last and the first negative disconnection first. Apply a thin film of anti-corrosion grease (petroleum jelly) to the finished connection. Tighten terminal bolts to the torque specified on the battery label or datasheet for that terminal type; do not over-tighten.
| Terminal type | Typical torque (N·m) | Typical torque (in·lb) |
|---|---|---|
| Bolt / insert M5 | 3–4 | 27–35 |
| Bolt / insert M6 | 5–6 | 44–53 |
| Bolt / insert M8 | 9–11 | 80–97 |
| Bolt / insert M10 | 14–20 | 124–177 |
Typical guidance values. Always follow the torque marked on the specific battery label or its datasheet, which takes precedence over this table. Re-check torque after the first weeks of service and at every scheduled inspection.
Loose or corroded connections cause local heating, voltage drop, and reduced capacity, and can lead to thermal runaway. Never connect a charger or load with reversed polarity.
Using the correct charger and settings is the single most important factor in battery life. Use a constant-voltage, current-limited charger (or a smart/microprocessor charger) with the correct AGM or GEL profile. If you are unsure whether your charger is suitable, contact ATB Power before connecting it.
| Mode | AGM | GEL | Per cell |
|---|---|---|---|
| Cyclic / boost (charge) | 14.4–14.7 V | 14.1–14.4 V | 2.40–2.45 / 2.35–2.40 VPC |
| Float / standby | 13.5–13.8 V | 13.6–13.8 V | 2.25–2.30 VPC |
| Max. charge current | ≤ 0.30 × C | ≤ 0.20 × C | C = rated Ah (C20) |
For 6V batteries use half these voltages; for a 2V cell use the per-cell figures. C is the rated 20-hour capacity in Ah. Always defer to the specific model datasheet where it gives different values.
Charge voltage must be corrected for temperature when the battery operates away from 25°C. Adjust by approximately −4 mV per cell per °C (about −24 mV/°C for a 12V battery; −2 mV/cell per °F). Increase voltage as temperature falls and decrease it as temperature rises. Many smart chargers do this automatically with a temperature sensor.
Overcharging drives gassing and dries out the electrolyte, which permanently damages a sealed VRLA battery. Do not exceed the recommended voltages, do not use an uncontrolled or flooded-type charger, and never use an equalization charge on a sealed VRLA battery unless ATB Power specifically directs it.
Cycle life depends strongly on how deeply the battery is discharged. Shallower cycles give many more cycles than deep ones. For best life in cyclic applications, keep the average discharge at or above 50% state of charge; avoid routinely discharging below 20% state of charge. Recharge promptly after every discharge.
Let the battery rest (no charge or load) for several hours, then read open-circuit voltage to estimate state of charge:
| State of charge | 12V battery | 6V battery | Per cell (2V) |
|---|---|---|---|
| 100% | ~12.8–12.9 V | ~6.4 V | ~2.14 V |
| 75% | ~12.6 V | ~6.3 V | ~2.10 V |
| 50% | ~12.3 V | ~6.2 V | ~2.06 V |
| 25% | ~12.0 V | ~6.0 V | ~2.00 V |
| 0% | ≤ 11.8 V | ≤ 5.9 V | ≤ 1.97 V |
Typical rest-voltage values for VRLA AGM/GEL at 25°C. Voltage under load reads lower; allow the battery to stabilize before judging state of charge.
Discharging far below the cut-off voltage, or leaving the battery connected to a parasitic load when not in use, can deeply discharge and damage it. Disconnect the load during long idle periods and keep the battery charged.
VRLA batteries are maintenance-free in the sense that they need no water addition. They still require periodic inspection to confirm safe, reliable operation.
For critical standby systems, perform a periodic capacity (discharge) test per the system standard. A battery that delivers less than 80% of rated capacity is normally considered end-of-life and should be replaced.
| Symptom | Likely cause | Action |
|---|---|---|
| Low capacity / short runtime | Undercharging, sulfation, age, low temperature | Recharge fully; check charger profile/voltage; test capacity; replace if <80% |
| Will not hold charge | Deep discharge, internal short, end of life | Attempt a full recharge; if voltage falls quickly, replace |
| Case swelling / heat | Overcharge, high voltage, thermal runaway | Stop charging; correct charger voltage/temp compensation; replace battery |
| One battery low in a bank | Uneven connections, weak unit | Re-torque, equalize cable lengths, replace the weak battery |
| Battery dry / vents opening | Chronic overcharge | Reduce charge voltage; verify charger; replace if performance lost |
The battery is hot to the touch, swelling, leaking, or venting. Disconnect the charger, ventilate the area, allow it to cool, and remove the battery from service.
ATB VRLA batteries are classified as non-spillable when they meet the relevant vibration and pressure-differential criteria, and are generally accepted for ground, sea, and air transport when terminals are protected against short circuit. Keep batteries upright, protect terminals, and ship in original packaging where possible. Confirm current carrier and dangerous-goods requirements before shipping.
| Parameter (per 12V, 25°C) | AGM | GEL |
|---|---|---|
| Cyclic / boost charge voltage | 14.4–14.7 V | 14.1–14.4 V |
| Float / standby voltage | 13.5–13.8 V | 13.6–13.8 V |
| Max charge current | ≤ 0.30 C | ≤ 0.20 C |
| Temp. compensation | −4 mV/cell/°C (−24 mV/°C per 12V) | |
| Recommended operating temp. | 20–25°C (68–77°F) | |
| Self-discharge | ~1–3% per month at 25°C | |
| Recharge in storage | Before OCV < 12.4 V, or every 6 months | |
| End-of-life capacity | < 80% of rated capacity | |
| Equalization | Not permitted unless directed by ATB Power | |
Operating the battery outside the conditions in this manual — including incorrect charger settings, overcharge, deep over-discharge, storage in a discharged state, or use of an AGM profile on a GEL battery (or vice versa) — can shorten its service life. For the correct settings for a specific model, or for technical support, contact ATB Power at info@atbpower.com or atbpower.com.
This manual provides general guidance for ATB VRLA AGM and GEL batteries. Where a specific battery datasheet or label states different values for voltage, current, or torque, those model-specific values take precedence. Specifications are subject to change without notice. © 2026 ATB Power.