What voltage should my battery run at?

There isn’t a single universal voltage for all batteries—the correct voltage depends on the battery’s chemistry, the number of cells in series, and whether you’re charging, resting, or under load. Use the per-cell targets and multiply by the number of cells in your pack, and always follow the manufacturer’s specifications.

How voltage is defined for battery packs

Voltage readings reflect the chemistry, the configuration of cells in series, and the battery’s state of charge. Nominal voltage is a typical or average value, while the full-charge voltage indicates the maximum safe voltage per cell. Resting voltage shows the state after a recent use or charging cycle, whereas under-load voltage can sag significantly. Chargers and battery management systems (BMS) enforce safe voltage limits to protect longevity and safety.

Chemistry-specific voltage targets

Lead-acid (including car and deep-cycle)

Lead-acid batteries are most commonly found in 12V packs. Each cell sits around 2.0–2.2V when discharging, with an overall nominal pack voltage near 12V. The resting full charge is typically about 12.6–12.8V, and charging voltages usually fall in the 13.8–14.4V range for a 12V battery during charging. Deep discharge protection keeps resting voltage above roughly 11.8–12.0V; float charging often sits around 13.5–13.8V for maintenance.

Before listing, consider these typical ranges for a standard 12V lead-acid pack (6 cells in series):

• Nominal pack voltage: about 12.0V (6 × ~2.0–2.12V per cell)


• Fully charged resting voltage: about 12.6–12.8V


• Charging voltage during use: commonly 13.8–14.4V


• Discharge cutoff (resting): about 11.8–12.0V under heavy use


• Long-term float/maintenance: about 13.5–13.8V for some AGM/Gel systems

Concluding: Use a charger compatible with your battery type and follow the maker’s guidelines. Monitor temperature and avoid prolonged overcharging or deep discharges.

Nickel-based chemistries (NiMH and NiCd)

NiMH and NiCd cells have a nominal voltage of about 1.2V per cell. They charge up to roughly 1.4V per cell, and they tend to drift lower under load. End-of-discharge per cell is typically around 0.9–1.0V. Pack voltage scales with the number of cells in series, so an 8-cell pack might run around 9.6V nominal, with full charge near 11.2V.

Before listing, here are common ranges per cell and for typical packs (examples):

• Nominal voltage per cell: 1.2V


• Full charge per cell: ~1.4V


• Typical end-of-discharge per cell: ~0.9–1.0V


• Example pack (8 cells): nominal ~9.6V; full ~11.2V


• Example pack (10 cells): nominal ~12.0V; full ~14.0V

Concluding: These chemistries are common in older devices and some cordless tools. Use the correct charger and avoid deep discharges to extend life.

Li-ion and Li-polymer (including pouch cells)

Lithium-ion and lithium-polymer cells typically run at a nominal 3.6–3.7V per cell and are charged up to 4.2V per cell. The safe operating window is commonly around 3.0–4.2V per cell. Discharging below 2.5–3.0V per cell can permanently damage the cell without protection circuitry. Multi-cell packs scale accordingly: a 2S pack is about 7.4V nominal, a 3S pack about 11.1V nominal, and a 4S pack about 14.8V nominal, with a maximum of 16.8V when fully charged (4.2V per cell).

Before listing, these are typical targets for Li-ion/Li-poly packs:

• Nominal voltage per cell: 3.6–3.7V


• Full charge per cell: 4.2V


• Typical operating range per cell: 3.0–4.2V


• Minimum per-cell voltage (protective cutoff): ~2.5–3.0V


• Pack examples: 2S ~ 7.4V; 3S ~ 11.1V; 4S ~ 14.8V; max pack voltages scale with cell count

Concluding: Always use a proper charger and a battery management system (BMS) for safety. Avoid exposing cells to voltages beyond manufacturer limits and monitor for heat or swelling.

LiFePO4 (LFP)

LiFePO4 cells have a nominal voltage near 3.2V and a higher safe full-charge voltage around 3.6–3.65V per cell. The typical minimum per cell is around 2.5–2.8V. A 4S LFP pack would nominally be about 12.8V, with a full charge around 14.4–14.6V and a resting voltage near 12.8V. LFP chemistry is known for stability and a longer cycle life, but it still requires correct charging limits and protection circuitry.

Before listing, common per-cell targets for LFP are:

• Nominal per-cell voltage: 3.2V


• Full charge per cell: 3.6–3.65V


• Minimum recommended per cell: 2.5–2.8V


• Pack example: 4S ~12.8V nominal; full ~14.4–14.6V

Concluding: Follow manufacturer guidance for LFP packs. They are typically safer at higher current and have different voltage tolerances than Li-ion.

Practical tips for choosing and using the right voltage

Voltage targets are only part of the picture. The battery’s chemistry, how many cells are in series, the state of charge, and the protection electronics all shape the correct operating voltage. Always consult the device or battery pack specifications, use the correct charger, and monitor for signs of distress such as swelling, overheating, or sudden voltage drops.

What this means for your device

In your device, the operating voltage is defined by the battery pack and its management system. When replacing a battery, match the exact chemistry and voltage specification from the manufacturer. If you’re building or modifying a pack, calculate nominal voltage by multiplying the per-cell voltage by the number of cells in series, and ensure charging limits align with the per-cell targets and the pack’s BMS.

Summary

Voltage is chemistry- and configuration-specific. There is no universal “correct” voltage for all batteries. By knowing the per-cell voltage targets, the number of cells in series, and the device’s charging guidance, you can determine the safe and effective operating voltage for your battery. Always prioritize manufacturer specifications and safety practices.

What should a 12 volt battery read when fully charged?

A fully charged 12-volt battery should read 12.6 volts or higher when at rest (with the engine off). Readings between 12.6 and 12.8 volts indicate a full charge, while a reading of 12.7 volts or more suggests a very full charge. After being fully charged, a car battery's voltage will drop to around 12.6 volts after it has rested for a few hours.
 
This video demonstrates how to test a 12V battery with a multimeter: 1mHSZ GarageYouTube · Aug 22, 2022
Voltage levels and charge state

• 12.6–12.8 V: Fully charged
• 12.4–12.5 V: Partially charged (about 75% charged)
• 12.0–12.3 V: Needs charging (about 50% charged)
• Below 12.0 V: Discharged 

Important considerations

• Resting voltage: The 12.6-volt reading is the "resting" voltage, which is measured after the battery has been disconnected from a charger and has had time to settle. 
• Engine running: When the engine is running, the alternator will boost the voltage to about 13.5 to 14.5 volts to keep the battery charged. 
• Load test: A simple voltage test can't reveal a battery's ability to hold a charge under load. A battery that reads 12.6 volts but drops significantly when a device is turned on may have a problem. 

What voltage is too low for a car battery?

A car battery is too low if it reads below 12.0 volts when the engine is off; this is considered fully discharged and needs to be recharged. A reading between 12.0 and 12.4 volts indicates the battery is partially charged and should be recharged soon, as running it at this level for too long can decrease its lifespan. If the voltage drops to or below 10.5 volts, the battery is essentially scrap and will not be able to start the engine.
 
This video explains what a 12-volt car battery should read when the engine is off: 38sMechanic MindsetYouTube · Mar 11, 2021
Voltage and charge levels (engine off) 

• $12.6$V or higher: Fully charged 
• $12.4$V: Approximately 60% charged 
• $12.0$V to $12.4$V: Partially discharged, needs recharging 
• Below $12.0$V: Fully discharged or "flat" 
• $10.5$V or lower: Critically low, likely damaged and considered "scrap" 

What to do if your battery is low

• Recharge the battery: If the voltage is between 12.0V and 12.4V, a full charge can restore it. 
• Check for problems: If the battery is low again after charging, it could be due to a number of issues: 
  • Alternator problems: The alternator may not be charging the battery correctly. 
  • Parasitic drain: Something in the car might be drawing power even when it's off. 
  • Old age: An old battery is more sensitive to low voltage and may be unable to hold a charge properly. 
• Consider replacement: If the battery voltage consistently falls below 12.0V, or if it shows other signs of failure (like taking multiple attempts to start), it's likely time to replace it. 

You can watch this video to learn how to check your car battery voltage with a multimeter: 1mHSZ GarageYouTube · Aug 22, 2022

What voltage indicates a bad battery?

It should drop no more than two volts while the engine cranks. If it drops any more or dips below 9.5 volts, you need a new battery.

Is 11.7 volts a dead battery?

Partially Discharged: A battery showing around 12.1 volts is approximately 50% charged, while a reading of about 11.7 volts indicates it's around 25% charged. Fully Discharged: A reading of 10.5 volts or lower usually indicates a dead or fully discharged battery.