AGM Battery Charging Settings for MPPT & PWM Controllers

Modified on Tue, 14 Oct at 12:35 AM

? AGM Battery Charging Settings for MPPT & PWM Controllers

Getting your charging voltages right is essential to maximise AGM battery lifespan and performance.
Incorrect settings can cause undercharging, sulfation, or even overcharging damage — especially in solar or DC-DC systems.

In this guide, you’ll learn the recommended charging settings for AGM batteries using MPPT and PWM solar controllers, along with temperature adjustments, charging stages, and a reference voltage chart for 12V, 24V, and 48V systems.

☀️ 1. Why Charging Settings Matter

AGM (Absorbed Glass Mat) batteries are sealed lead-acid batteries that use absorbed electrolyte, meaning they can’t be topped up with water.
That’s why precise voltage control is critical — once the electrolyte dries out or plates sulfate, capacity loss is irreversible.

Proper charging ensures:

✅ Maximum cycle life
✅ Full charge capacity
✅ Reduced sulfation buildup
✅ Stable voltage for inverters and 12V appliances

⚙️ 2. MPPT vs PWM: What’s the Difference?

Controller Type	How It Works	Best For	Efficiency
MPPT (Maximum Power Point Tracking)	Adjusts input voltage and current for maximum solar yield.	Larger off-grid and high-efficiency setups.	⭐⭐⭐⭐⭐
PWM (Pulse Width Modulation)	Connects solar panel voltage directly to battery via pulsed output.	Budget or small systems under 300W.	⭐⭐⭐

? Tip: If you’re running high-power solar arrays (300W+), MPPT controllers are strongly recommended for AGM batteries due to better charge control and efficiency — especially in variable sunlight.

⚡ 3. AGM Battery Charging Stages

Both MPPT and PWM chargers operate using three main charging stages:

Bulk Stage:
- Charger delivers maximum current until voltage reaches the absorb setpoint.
- Fills battery to ~80–90%.
Absorption Stage:
- Voltage held constant (≈14.4–14.7V for 12V battery).
- Current gradually tapers as the battery nears full capacity.
Float Stage:
- Voltage reduced to 13.5–13.8V to maintain full charge safely.
- Prevents overcharging during long-term connection.

Optional fourth stage (if charger supports it):
4. Equalization (Optional for AGM)

Gently desulfates plates at 14.8V–15.0V occasionally.
Use only if manufacturer allows it — overdoing equalization can shorten AGM life.

? 4. Recommended AGM Charging Settings

Below are safe, universal settings for most AGM deep cycle batteries in off-grid, caravan, and RV systems.
Always confirm with your specific battery’s datasheet if available.

? 12V AGM Battery

Charging Stage	Voltage Setting	Notes
Bulk / Absorption	14.4 – 14.7V	Primary charging voltage
Float	13.5 – 13.8V	Maintains full charge
Equalization (if allowed)	14.8V (max)	Use rarely – for desulfation only
Low Voltage Disconnect (LVD)	11.0 – 11.2V	Disconnect loads below this level
Reconnect Voltage	12.6V	Reconnect loads when charged

? 24V AGM Battery

Charging Stage	Voltage Setting	Notes
Bulk / Absorption	28.8 – 29.4V	Same principle, doubled voltage
Float	27.0 – 27.6V	Maintenance charge
Equalization (if allowed)	29.6V – 30.0V	Occasional, only if recommended
Low Voltage Disconnect	22.0 – 22.4V	Prevents deep discharge
Reconnect Voltage	25.2V	Resume charging threshold

? 48V AGM Battery

Charging Stage	Voltage Setting	Notes
Bulk / Absorption	57.6 – 58.8V	High-voltage systems
Float	54.0 – 55.2V	Maintenance stage
Equalization (if allowed)	59.2V – 60.0V	Controlled equalization
Low Voltage Disconnect	44.0 – 44.8V	Battery protection
Reconnect Voltage	50.4V	System recovery

?️ 5. Temperature Compensation

Charging voltages change with temperature.
AGM batteries prefer slightly lower voltage in hot conditions and higher in cold conditions.

Temperature	Adjustment
Above 30°C	Subtract 0.03V per °C from charge voltage
Below 20°C	Add 0.03V per °C to charge voltage

? Example:
If your bulk voltage is 14.6V at 25°C, and it’s 35°C ambient →
14.6V – (0.03V × 10°C) = 14.3V optimal setting

Most quality MPPT controllers (like Victron or EPEVER) handle this automatically via a temperature sensor.

? 6. How to Verify Your Charger Settings

Before connecting your battery:

Access the controller settings (via LCD or app).
Check the battery type is set to AGM or Sealed Lead-Acid (SLA).
Verify voltages for bulk, float, and LVD match the chart above.
If using multiple batteries, confirm they’re wired and balanced correctly.
After first full charge, measure battery resting voltage after 12 hours — should read 12.7–12.9V (full).

⚠️ 7. Common AGM Charging Mistakes to Avoid

❌ Using Lithium (LiFePO4) charge profile – too low float, damages AGM.
❌ Leaving charger in “equalize” mode too long – can overheat plates.
❌ Running without temp compensation – overvoltage in summer, undercharge in winter.
❌ Undersized solar array – causes chronic undercharging and sulfation.
❌ Over-discharging below 11V – permanently reduces capacity.

? 8. Pro Tips for Long AGM Battery Life

✅ Use a smart MPPT charger with adjustable voltage profiles.
✅ Always recharge to 100% at least once per week.
✅ Keep battery temperature between 15–30°C where possible.
✅ Avoid storing below 12.4V for long periods.
✅ Check float voltage annually and recalibrate if needed.
✅ Use a battery monitor to track cycles and charge efficiency.

? 9. Quick Reference Voltage Chart (12V AGM Battery)

Battery Condition	Voltage (Resting)	State of Charge (Approx.)
100% (Full)	12.8 – 12.9V	Fully charged
90%	12.7V	Optimal
75%	12.5V	Acceptable
50%	12.2V	Recharge soon
25%	12.0V	Avoid going below
0%	11.8V or less	Risk of damage

? 10. Summary: Recommended Settings at a Glance

System Voltage	Bulk / Absorb	Float	Equalize (if used)
12V	14.4–14.7V	13.5–13.8V	14.8V max
24V	28.8–29.4V	27.0–27.6V	29.6V max
48V	57.6–58.8V	54.0–55.2V	59.2V max

? Key Takeaway

For AGM batteries, the right charging voltage is the difference between 2 years and 6+ years of reliable life.
Set your MPPT or PWM controller carefully, recharge fully and frequently, and avoid over-discharge.

Well-tuned charge settings will ensure your AGM deep-cycle battery performs efficiently through thousands of camping trips and off-grid adventures.