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Battery voltage

What sort of reading should my gauge on the instrument panel show when turning on the ignition? It's reading 10 now and jumps to 14 when the engine is running. Battery performance seems poor hence the question.

Asked by: Paul Taylor  | 4.14pm, Monday 18 September


WW says:

Resting voltage of a fully charged 12V lead acid battery at rest of 12.7V or above. When the engine is running it will rise to 14V or above (not more than 15V usually). If the battery is fully charged using the voltmeter on the dashboard (or better, with a multimeter directly at the battery terminals) it will be 12.7V or a little above. With no load, if the voltage is 12.1V, the battery is around half-charged and should never be allowed to drop below 12V (as permanent damage will occur). Under load, the voltage will drop depending on the power being drawn from the battery. However if your battery is showing 10V at rest then it's effectively dead.

Mark Langley  | 7.49PM, Monday 18 September

Also if the voltage rises very quickly to !4V it indicates that the battery is not taking charge properly; at the end of its useful life.

Rupert Smedley  | 1.20PM, Wednesday 20 September


Readers say:

Also wait several hours after the battery has been charged for an accurate indication of SOC, or until a load has been applied for a while, difficult to say how long or what load, the voltage will be artificially high after charging due to what's called surface charge. You need it decay for the voltage to stabilise.

Steve Buckley  | 8.09PM, Friday 20 October

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