Battery went dead - now check engine light on

[josiahg52]

From Chat: Some AGM designs have charging requirements that differ from flooded batteries, but the Duracell/East Penn AGM does not require an unusually high vehicle charging voltage. East Penn specifically approves it for conventional automotive charging systems operating around 13.8–14.4 V.

From me: I think I can use my OBD2 reader and my Carista app to see what charging voltage the vehicle is delivering

As someone who has been involved with batteries for 25 years, the real answer is: it’s complicated.

AGM charging requirements are generally very similar. There can be some variation depending on whether the battery is VRLA or maintenance-free, the type of lead used, the number of plates, and other aspects of its construction. The specific charging voltages are also dependent on battery temperature.

AGMs generally benefit from higher charging voltages during bulk, absorption, and float charging. The Duracell AGM is no different from other AGM batteries in this respect. It is not some special AGM manufactured by East Penn for the Duracell brand that has fundamentally different charging requirements.

AGM automotive battery manufacturers want to sell batteries, so naturally they specify charging-voltage ranges that reflect what automotive charging systems actually operate at. That does not necessarily mean every voltage within those ranges is optimal for the battery. At the end of the day, it is still a 12V lead-acid battery and will operate over a fairly broad range.

If the question to the AI was something like:

“I replaced the factory flooded battery in my 2025/2026 4Runner with a Duracell AGM. Someone says an AGM needs higher charging voltage. Will the 4Runner charge it properly?”

Then the AI could reference East Penn or general automotive AGM specifications and give a technically defensible answer:

“A Duracell AGM can replace a flooded battery in a typical 13.8–14.4V automotive charging system.”

In fact, the majority of automotive AGM batteries will operate perfectly fine in these systems. Whether the battery is being charged optimally is a different question, and that really depends on the particular vehicle’s charging system and how it manages the battery.

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[bobholthaus]

As someone who has been involved with batteries for 25 years, the real answer is: it’s complicated.

AGM charging requirements are generally very similar. There can be some variation depending on whether the battery is VRLA or maintenance-free, the type of lead used, the number of plates, and other aspects of its construction. The specific charging voltages are also dependent on battery temperature.

AGMs generally benefit from higher charging voltages during bulk, absorption, and float charging. The Duracell AGM is no different from other AGM batteries in this respect. It is not some special AGM manufactured by East Penn for the Duracell brand that has fundamentally different charging requirements.

AGM automotive battery manufacturers want to sell batteries, so naturally they specify charging-voltage ranges that reflect what automotive charging systems actually operate at. That does not necessarily mean every voltage within those ranges is optimal for the battery. At the end of the day, it is still a 12V lead-acid battery and will operate over a fairly broad range.

If the question to the AI was something like:

“I replaced the factory flooded battery in my 2025/2026 4Runner with a Duracell AGM. Someone says an AGM needs higher charging voltage. Will the 4Runner charge it properly?”

Then the AI could reference East Penn or general automotive AGM specifications and give a technically defensible answer:

“A Duracell AGM can replace a flooded battery in a typical 13.8–14.4V automotive charging system.”

In fact, the majority of automotive AGM batteries will operate perfectly fine in these systems. Whether the battery is being charged optimally is a different question, and that really depends on the particular vehicle’s charging system and how it manages the battery.

Thank you for that info; it's always good to learn from someone that knows more than I do. I appreciate it.