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.