How do I properly store a battery?

Periods of inactivity can be extremely harmful to lead-acid batteries. When placing a battery into storage, follow the manufacturer’s recommendations and/or the recommendations below to ensure that the battery remains healthy and ready for use.

The most important things to avoid:

  1. Freezing. Avoid locations where freezing temperatures are expected. Keeping batteries at a high state of charge will also prevent freezing. Freezing results in irreparable damage to battery plates and containers. NOTE that if a battery is kept completely charged, the chances of freezing are minimal.
  2. Heat. Avoid direct exposure to heat sources, such as radiators or space heaters. Temperatures above 80°F / 26°C accelerate the battery’s self-discharge characteristics. NOTE that heat causes more damage to a battery than cold ever will so keep your battery storage area as cool as reasonably possible.
  3. NOTE that storing your battery on concrete will not damage your battery!

Step-by-step storage procedure

  1. Completely charge the battery before storing
  2. Store the battery in a cool, dry location, protected from the elements
  3. During storage, monitor the specific gravity (flooded) or voltage. Batteries in storage should be given a boost charge when they show a charge of less than 75% or approximately 12.40 volts for a 12-volt battery. 
  4. Completely charge the battery before re-activating
  5. For optimum performance, equalize the batteries (flooded) before putting them back into service. Refer to the Equalizing section for this procedure

How fast will an AGM or GEL battery lose its charge sitting in storage?

AGM and GEL batteries will have a self-discharge or internal electrochemical “leakage” of between 1% and 15% per month, depending on storage temperature. This internal or self-discharge rate will cause the battery to become sulphated and fully discharged over time. High temperatures accelerate the process so that a battery stored at 86°F (30°C) will self-discharge twice as fast as one stored at 68°F (20° C).

Discover AGM or GEL batteries will naturally discharge at approximately:

  • 1%-2% per month when stored at 8˚C/46˚F
  • 3%-4%% per month when stored at 20˚C/68˚F
  • 5%-6% per month when stored at 30˚C/86˚F
  • 10%-12% per month when stored at 40˚C/104˚F

By comparison, a quality flooded deep-cycle battery will have a self-discharge rate at least two times greater than AGM or GEL batteries.

  • Check and charge, if required, your Deep-cycle AGM or GEL batteries every 2 – 3 months.
  • Check and charge, if required, your Deep-cycle wet Flooded batteries every 2 – 4 weeks.

Can I store my battery on a concrete floor?

A hundred years ago, when battery cases were made of porous materials, such as wood, storing batteries on concrete floors would accelerate their discharge. This is no longer a problem as modern battery cases, made of polypropylene or hard rubber, are sealed against external leakage, which causes the discharge. However, the top of the battery must be kept clean and dry. Temperature stratification within large batteries could accelerate the self-discharge if the battery is sitting on a cold floor in a warm room or is installed in a submarine.

Can I store my battery in my garage during the winter, or will it freeze?

Provided the batteries are maintained in a fully charged status, batteries can be stored in temperatures as low as -25°F without freezing.

What do I do if I have to store my batteries outside for winter?

AGM and GEL VRLA DRY CELL batteries can easily be stored in sub-freezing temperatures as low as -30°F/-35°C or lower as long as they are fully charged before storage. The same goes for flooded batteries.

The self-discharge rate of fully-charged AGM and GEL batteries is very low in these conditions, and they will not require charging for many months. Flooded batteries have higher self-discharge rates, so they may require top charging sooner. If your AGM or GEL batteries do freeze, they most likely will not recover. To attempt recovery, bring them inside and let them sit until the temperature of the inside of the battery reaches the temperature of the room it is in (approx. 20°C/68°F). Then, charge the batteries normally. DO NOT ATTEMPT TO CHARGE THEM UNTIL THE INTERNAL TEMPERATURE IS EQUAL TO ROOM TEMPERATURE. You may have to cycle the battery several times before deciding on its final condition.

If a flooded battery freezes – because it has excess water volume – it will probably freeze solid, expand, break the plates and even crack the case. A flooded battery that freezes is not typically recoverable.

Table 1 - Electrolyte Freezing Point

 Digital Voltmeter  State of Charge  Hydrometer Reading  Electrolyte
 Open Circuit Voltage  Approximate  Specific Gravity  Freezing Point
 >12.65  100%  1.265  -75°F (-59.4°C)
 >12.45  75%  1.225  -55° F (-48.3° C)
 >12.24  50%  1.190  -34° F (-36.7° C)
 >12.06  25%  1.155  -16° F (-26.7° C)
 >11.89  Discharged  1.120  -10° F (-23.3° C)


Why do Discover VRLA DRY CELL AGM and GEL batteries have an excellent shelf life?

Discover uses higher quality superior grids, premium separators and pure electrolytes, which prevent high self-discharge rates. Impurities in the lead alloy, separators and electrolyte cause tiny currents inside a cell, eventually discharging the battery and shortening its shelf life. Premium inter-cell welds block the slight cell-to-cell currents that cause self-discharge.