Know how to extend the life of a lead acid battery and what the limits are.
Adding chemicals to the electrolyte of flooded lead acid batteries can dissolve the buildup of lead sulfate on the plates and improve the overall battery performance. This treatment has been in use since the 1950s (and perhaps longer) and provides a temporary performance boost for aging batteries. It’s a stopgap measure because in most cases the plates are already worn out through shedding. Chemical additives cannot replace the active material, nor can cracked plates, corroded connectors or damaged separators be restored with an outside remedy.
Elevated self-discharge is a common failure mode with older batteries. With the shedding of the active material to the bottom of the container, a conductive layer forms that gradually fills the allotted space in the sediment trap. The now conductive liquid may reach the plates, creating a soft short. The shedding also causes the internal resistance to increase, reducing current handling.
Extending the service life of an aging battery can be useful as additives are cheap, readily available and worth the experiment for a handyman. These salts may reduce the internal resistance to give a sulfated battery a few extra months of life. Suitable additives are magnesium sulfate (Epsom salt), caustic soda and EDTA (EDTA is a crystalline acid used in industry).
When using Epsom salt, follow these easy steps to treat most starter batteries. Heat about 250ml (8 fl oz or a cup) of distilled water to about 66ºC (150ºF), mix in as much Epson salt as the water can absorb (a few tablespoons) and stir until dissolved. Avoid using too much salt because heavy concentration increases corrosion of the lead plates and the internal connectors.
When pouring the warm solution into the battery, the electrolyte level will raise. Do not remove electrolyte, and only add as much additive as the battery can take. Be careful not to overfill. Do not place un-dissolved Epsom salt directly into the battery because the substance does not dissolve well. In place of Epsom salt, try adding a pinch of caustic soda. Charge the battery after service. The results are not instantaneous and it may take a month for the treatment to work. The outcome is not guaranteed.
Batteries have improved, and additive treatments may be most effective with older battery models, expanding their life by a few months until a replacement is on hand. Modern batteries already include additives that reduce sulfation and corrosion. Industrial users seldom rely on remedial additives to prolong battery life as the system becomes maintenance prone.
Last updated 2017-03-07
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