What Do STD, AGM, and Gel Mean On a Battery Charger

Older lead-acid battery chargers were simple, robust, and reliable and they did their job, more or less, good. Internally, they had just a transformer, a few diodes, capacitors, and an analog Ammeter, and that was mostly all.

Modern smart battery chargers are microprocessor-controlled devices that come with many more features and options than the battery chargers just a few years ago - and all those features and options can lead to confusion, including labels like STD, AGM, Gel, Lithium, ENHC, Calcium, etc.

Updated: March 22, 2024.

Advanced Battery Chargers Features and Specifications

In order to prolong the operating lifetime of the batteries, microprocessor-controlled intelligent battery chargers are used.

Before the charging process even begins, such battery chargers must be set properly by the user in order to charge the battery in the most efficient way, taking into account the battery type, battery condition, temperature, and similar.

After being properly set, advanced battery chargers analyze the battery and charge it according to the options set by the user and by the result of its own analysis.

The most common battery charger options include:

• STD means standard wet or flooded lead-acid battery,
• AGM means Absorbent Glass Mat lead-acid battery,
• Gel means Gel-Cell lead-acid battery, or simply gel battery.

Although wet/flooded, AGM, and Gel batteries are all lead-acid batteries based on the same chemistry, their charging end voltages differ slightly.

By setting the lead-acid battery type, advanced battery chargers charge these lead-acid batteries to their 100% capacity, avoiding overcharging and undercharging.

Other common options include:

• Lithium means that the battery charger can be set to charge the lithium batteries - such batteries are charged using a different charging algorithm than the lead-acid batteries. This charging algorithm is usually described as a Constant Current / Constant Voltage (CC/CV) charging algorithm and is optimized for charging lithium batteries.
• Calcium means charging mode for the lead-acid batteries with the calcium-lead alloy plates. Calcium lead-acid batteries can be wet/flooded, AGM or Gel-Cell, so it is highly recommended to check the documentation of the battery to see recommended charging mode.
• Float means charging mode optimized for the batteries used in float/standby applications.
• Cycle means charging mode optimized for the batteries used in deep cycle applications.

Note that many advanced battery chargers come with some specific labels, features, and options.

For example, the Solar PL2320 6V/12V Advanced Battery Charger (Amazon link, link opens in the new window) control panel options include:

• PWR Supply present or not,
• 6V/12V: voltage of the charged battery,
• GEL, AGM, STD: type of the lead-acid battery,
• % Charge: charge percentage of the charged battery,
• Voltage: current charging voltage.

Solar PL2330 also comes with several self-explanatory additional status lights, allowing the user to monitor the battery charging process.

Similarly, the NOCO Genius G26000 12V/24V 26 Amp Pro-Series Battery Charger and Maintainer (Amazon link, link opens in the new window) control panel includes:

• Jump Charge is a mode of fast battery charge when the battery is charged quickly in order to enable it to crank the battery thanks to the increased battery "surface charge".
• 12V Norm Mode: for charging of the 12V wet/flooded, Gel-Cell, Enhanced flooded, maintenance-free, and calcium batteries.
• 12V Cold/AGM Mode: for charging of the 12V batteries in low temperatures below 50ºF (10ºC) or AGM batteries.
• 24V Norm Mode: for charging of the 24V wet/flooded, Gel-Cell, Enhanced flooded, maintenance-free, and calcium batteries.
• 24V Cold/AGM Mode: for charging of the 24V batteries in low temperatures below 50ºF (10ºC) or AGM batteries.
• 12V Repair Mode: an advanced battery repair/recovery mode.
• 13.6V Supply Mode: battery charger acts as a power supply.
• 16V AGM Racing Mode: for charging 16V AGM batteries (that are commonly used in racing applications).
• 16V Lithium Racing Mode: for charging 16V Lithium batteries (that are commonly used in racing applications).
• 12V AGM+ Mode: for charging of the 12V advanced AGM batteries (which require a slightly higher than normal charging voltage).
• 12V Lithium Mode: for charging of the 12V lithium batteries.

Also, NOCO Genius G26000 features a battery charge meter, allowing the user to see the actual battery charge.

The newer NOCO GENIUSPRO25 25A Smart Car Battery Charger (Amazon link, opens in the new window) comes with a similar control panel, which includes:

• 6V, 12V, 24V: wet/flooded, gel, enhanced flooded, maintenance-free, and calcium lead-acid batteries,
• 6V, 12V, 24V: AGM lead-acid batteries,
• 6V, 12V, 24V: Lithium Iron Phosphate (LiFePO4) batteries,
• 6V, 12V: Force Mode,
• 12V, 24V: Supply Mode,
• 6V, 12V, 24V: Repair Mode,
• 5A: decreased charging current from 25A to 5A, suitable for smaller batteries.

The more advanced the battery charger is, it supports more charging modes, more battery chemistries, more battery voltages, etc.

Thus, when your new battery charger arrives, be sure to read the Owner's Guide and get accustomed to your new unit.

Additional Modes and Warnings

Here are some of the additional models and warnings that some battery chargers may display/show to the users:

What does SUL mean on a battery charger?

"SUL" means that the battery charger has detected a sulfated battery and that it will go into desulfation mode.

What does FLO mean on a battery charger?

"FLO" means that the battery charger is in the float charging mode.

What does PD mean on a charger?

"PD" stands for "USB-C Power Delivery," an USB-C based fast charging technology, commonly used in newer smartphones, power banks, and similar devices.

Long Story Short: As one can see, advanced battery chargers may come with many, often very specific features and labels.

So, when You buy a new battery charger, it is highly recommended to thoroughly read the Owner's Guide and to get accustomed to your new unit.

Battery chargers, and especially the batteries they are charging, are able to provide huge currents that can damage things, cause injuries, or worse. So, whatever You do, stay safe.