Is 11.8 volts a dead battery?
11.8 volts is typically a discharged or severely weakened lead‑acid battery and is not reliable for starting a vehicle. It can sometimes be revived with proper charging and testing, but it often indicates the battery needs replacement, especially if it cannot hold a charge after a full recharge.
What 11.8 volts means for a 12-volt lead-acid battery
Lead‑acid car batteries are rated by their resting voltage when no load is applied. Full charge sits around 12.6 volts or higher, while lower readings imply a diminished state of charge. Temperature and battery age affect these numbers, so readings can drift with weather or hours since the last use. A resting voltage near 11.8 volts generally signals a battery that is discharged or dying, and it may sulfates if left in that condition for long. If the battery reads 11.8 volts under load or while starting, it is even less capable and likely needs immediate attention).
How to interpret common resting voltage ranges
These ranges are typical for a standard 12‑volt lead‑acid battery at rest, measured with no load and at moderate room temperature:
- 12.6V or higher: Fully charged and healthy
- 12.4–12.6V: High state of charge (roughly 75–100%)
- 12.2–12.4V: Moderate state of charge (roughly 50–75%)
- 12.0–12.2V: Low to moderate charge (roughly 25–50%)
- 11.9V or lower: Discharged or failing; risk of sulfation or aged cells
In short, 11.8 volts sits below the healthy range and indicates the battery is not ready to reliably start a vehicle without recharging and testing.
What to do if you measure 11.8V
If you see 11.8 volts, take a careful, step‑by‑step approach to determine whether the battery can be revived or should be replaced. The following steps help distinguish a recoverable battery from one that needs replacement.
- Ensure safety: Park on level ground, engage the parking brake, wear eye protection, and avoid sparks or flames near the battery.
- Charge the battery with a smart charger or maintainer, following the manufacturer’s instructions. Use a charger with a proper charge profile for flooded or AGM batteries.
- After charging, let the battery rest for several hours (ideally overnight) and re‑measure the resting voltage.
- Perform a load test or have a shop perform one. A battery that cannot sustain voltage under load is unlikely to be reliable even after a charge.
- Inspect battery terminals and cables for corrosion, looseness, or damaged insulation; clean or repair as needed.
- Test the charging system (alternator and wiring) to ensure the alternator can replenish the battery when the engine runs. A failing alternator can make a good battery look bad.
- Decide on replacement: If the battery cannot hold a charge or repeatedly falls back to low voltage, replacement is the safer option.
If, after charging and testing, the battery cannot hold a healthy resting voltage (typically around 12.6V) or falls again under a small load, replace it. Replacing a failing battery improves reliability and reduces the risk of roadside outages.
Summary
11.8 volts is generally not a healthy reading for a 12‑volt lead‑acid car battery. It usually indicates a discharged battery that needs charging and testing to determine whether it can be revived or should be replaced. Always measure the voltage with the engine off and the battery rested, consider the temperature, and follow up with a load test and a charging system check to avoid guessing about reliability. Regular maintenance and timely replacement extend the chances of starting reliably when you need it most.
Is 11.8 low for a car battery?
Below 11.8 volts – Battery is deeply discharged and may need to be replaced.
Is 11.8 V too low?
Anything below 12.0V is low. Below 11.8V is considered critically low.
Is 11.8 a dead battery?
A car battery is dead if its voltage is between 11.75 and 11.89 volts. Any reading between this interval means the battery is no longer working and a car owner should consider a replacement.
Will a car start with 11.8 volts?
Yes, 11.811.811.8 volts is often just enough to start a car, but it indicates a low charge that may lead to a difficult start and is the threshold for a weak battery. A fully charged battery should be between 12.612.612.6 and 12.912.912.9 volts. If the voltage is at or below 11.811.811.8 volts before starting, the battery may be weak, close to failure, and it's advisable to consider a recharge or replacement.
What to know about 11.811.811.8 volts
- May start, but poorly: A reading of 11.811.811.8 volts suggests the battery is somewhat discharged. It might start the car, but it could be a sluggish start.
- A sign of weakness: A battery voltage that reads 11.811.811.8 to 12.012.012.0 volts indicates it's not fully charged and is often considered weak.
- Risk of failure: If the voltage dips below 11.811.811.8 volts before starting, the battery is weak and could fail to start the car.
- Normal voltage: A fully charged battery at rest typically reads between 12.612.612.6 and 12.912.912.9 volts.
- After starting: A healthy car's alternator will charge the battery to around 13.513.513.5 to 14.514.514.5 volts while running.
What you should do
- Try to start the car and see if it turns over.
- If it starts with difficulty, consider turning off unnecessary electronics like the radio and air conditioning to reduce the initial load on the battery.
- If you can, try to get the battery recharged soon. If it cannot hold a charge and repeatedly reads below 11.811.811.8 volts, you should have it tested and likely replaced.
