How fast do lead acid batteries charge?

Firstly we need to categorise into different products;

  1. SLI (Starter lighting and ignition) Flooded Traction Semi traction, and leisure
  2. VRLA (Valve regulated lead acid) Which comprises of AGM (absorbed glass mat) and Gel (electrolyte held in a thixotropic gel)
  3. Pure Lead (Odyssey)

SLI Flooded Traction and leisure

Recommended charging at 10% of the Ampere hour rate e.g. 100 Ampere Hour battery would require 10 amps. If one assumes the battery was 80% discharged it would need 80 amps plus possibly (depends on the battery) another 10% for inefficiency to regain full charge. It makes sense to assume that 10 amps for 8.8 hours would be sufficient for a full charge. This is not the case as the voltage of the battery increases so the amperage will fall (Ohms Law) The normal “rule of thumb” that is applied in this case is 8(amps) x 10 (hours) gives 80% charge and the amount of time take to get to 80% should be added on (in this case a further 10 hours) for battery to regain a full state of charge.

VRLA batteries require a minimum of 10% and a maximum of 25% charge obviously charge quicker and tend to be more efficient so 100 Ah battery 25 amp charge rate will charge for 4 hours to 80% + 4 hours.

Pure Lead even better requiring 40% at minimum and theoretically almost no upper limit so 100 Ah battery charged at 40 amps will be at 80% in two and a half hours and fully charged in five hours. It is possible with Odyssey to take a 100ah battery charge it at 200amps and have the battery back in service in 1 hour!

It may be useful to point out that the batteries listed do tend to have different charging algorithms and advice should always be taken on the correct battery charger contact us at www.countybattery.co.uk

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