Charging 12V Batteries: Best Practices

CTEK multi battery charger

This is a guest article written by Alan Knight, one of the more frequent contributors to this website.

What Happens to Batteries when you Overcharge them?

Do not attempt to charge a 12v battery with anything other than a 12v charger, whether it is a flooded unit, Sealed Lead Acid (SLA), gel or AGM. SLA and AGM batteries require a charge rate of about 1/10th of its Amp-hour rating.  If you charge at a higher rate the battery can build up excessive heat and start to ruin.

In a Gel unit, airways will form over time in the gel silica.  The gel hardens when it gets too hot and once it hardens it has a reduced ability to transform soft lead sulphate back to sulphuric acid thus reducing the surface area that the plates contact with the electrolyte.  This means less of the plate can take part in the discharge - recharge chemical reaction.

An AGM battery will over heat and expel the electrolyte.  The electrolyte transforms into gas and is able to escape through the one way valve and reduce the unit to scrap as it boils due to no liquid to cool it down.

A flooded unit will also overheat and buckle the end plates.  This is clearly visible through a bulging on the side of the unit, although this will take a few months of constant over charging to achieve as batteries charging voltages are graded to a minimum and not a maximum.

What Type of Battery Charger Should You Use?

Use a three or five stage charger which incorporates an automatic 15v-16v equalization charge and your battery will last for years longer than its warranty.  Stay away from the cheap 4-6 Amp chargers since these are unregulated and can destroy your battery very quickly.

When charging allow the electrolyte to mix by bubbling.  Contrary to some literature, this is not the sign of a defective battery.  It is the reason that there are vents on batteries - to allow any gas pressures that may build up during the process to escape without causing any explosions.

Related posts:

  1. How to Charge Two 12 Volt Batteries with One Charger
  2. How to Connect Two 12 Volt Batteries in Series for 24 Volts
  3. Connecting Batteries in Series and Parallel at the Same Time
  4. How to Make 36 Volts from 12 Volt Batteries
  5. 24 Volt Battery Equalizer Install

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Related posts:

  1. How to Charge Two 12 Volt Batteries with One Charger
  2. How to Connect Two 12 Volt Batteries in Series for 24 Volts
  3. Connecting Batteries in Series and Parallel at the Same Time
  4. How to Make 36 Volts from 12 Volt Batteries
  5. 24 Volt Battery Equalizer Install
2 Responses to Charging 12V Batteries: Best Practices
  1. Steve Voorhis
    October 20, 2011 | 9:17 am

    When trying to follow instructions, I get a lot of sparks and heat whenever I try to connect the positive to the negative between two 12 volt batteries. No damage yet, but why is this happening?( I have the other side all ready connected positive to negative.)I’m trying to make a 24v power supply to test a motor.

    • Liza
      May 19, 2012 | 7:12 pm

      Lavoro per il domani uno sgdaruo di Yesturdays ad alcuni esempi c8 stato indicato questo esempio, via David hardvalder sopra Twitter e trovato esso per essere molto informativo ed ugualmente il punto

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