The recommended storage temperature for most batteries is 15°C (59°F) usually in a cool, dry place; the extreme allowable temperature is –40°C to 50°C (–40°C to 122°F) for most chemistries. If you’re still worried, You can also use a battery storage case or bag to help keep it insulated.
Lead-acid Battery Storage
Sealable lead acid batteries may be kept in storage for up to two years. Because all batteries gradually self-discharge over time, it is critical to monitor the voltage and/or specific gravity and then administer a charge when the battery reaches 70% state-of-charge, which is 2.07V/cell open circuit or 12.42V for a 12V pack. (At 70% charge, the specific gravity is approximately 1.218.) Lead acid batteries may have varying readings, so consult the manufacturer’s instruction manual. Some battery manufacturers may allow a lead acid battery to deplete to 60% before charging.
After prolonged storage, sulfation may preclude charging small sealed lead acid cells. These batteries are frequently reactivated by applying a high voltage. Initially, the cell voltage under charge may reach 5V while drawing very little current. The charging current turns the big sulfate crystals into active material after about 2 hours, the cell resistance reduces, and the charge voltage eventually normalizes. The cell can accept a typical charge between 2.10V and 2.40V. Set the current restriction to a very low level to avoid damage. Do not attempt to perform this service if the power supply does not have current limitations.
Nickel Metal Hydride Battery Storage
Nickel metal hydride battery can be kept for up to 3-5 years. Priming can partially reverse the capacity reduction that happens during storage. Nickel-cadmium is easily stored. After priming, the US Air Force was able to deploy NiCd batteries that had been in storage for 5 years with good recoverable capacities. Priming is thought to be necessary when the voltage falls below 1V/cell.
On nickel-based batteries, measuring SOC by voltage is problematic. Voltage is affected by a flat discharge curve, agitation after charge and discharge, and temperature. The good news is that the charge level for storage is not crucial for this chemistry, so if the battery is empty, simply charge it and store it in a cool, dry spot. Priming should be faster with some charge than if kept completely discharged.
Storage at roughly 40% state-of-charge is recommended (SOC). This minimizes capacity loss due to aging while keeping the battery operational and allows for some self-discharge. Nickel-based batteries can be stored fully discharged with no adverse effects.
Lithium-ion Battery Storage
Primary alkaline and lithium batteries can be stored for up to 10 years with only moderate capacity loss. There is almost little self-discharge below roughly 4.0V at 20°C (68°F); storing below 3.7V results in incredible lifetime for most Li-ion devices. Finding the exact 40-50 percent SOC threshold for Li-ion storage is not critical. At 40% charge, most Li-ion batteries like the GeePower have an OCVof 3.82V/cell at normal temperature. Rest the battery for 90 minutes before taking the reading to ensure you receive the right result after a charge or drain. If this is not practical, overshoot the discharge voltage by 50mV or go 50mV higher on charge. This means discharging to 3.77V/cell or charging to 3.87V/cell at a C-rate of 1C or less. The rubber band action will bring the voltage down to around 3.82V. Figure 1 depicts a typical Li-ion battery discharge voltage.
Figure 1: Discharge voltage as a function of state-of-charge
The battery SOC is reflected in the OCV. At 40% SOC (25°C), lithium manganese oxide reads 3.82V, whereas at 30% SOC, it reads around 3.70V. (shipping requirement). The reading is influenced by temperature as well as prior charge and discharge actions. Allow the battery to rest for 90 minutes before taking the reading.
Li-ion batteries cannot be submerged in water for an extended period of time. Copper shunts form inside the cells, causing an increase in self-discharge or a partial electrical short. If the cells are recharged, they may become unstable, creating excessive heat or other irregularities. Li-ion batteries that have been stressed may still perform normally, but they are more vulnerable to mechanical damage. The user should bear the risk of improper handling, not the battery manufacturer.
Capacity Loss during Storage
Storage causes two types of losses: self-discharge, which can be recharged before use, and non-recoverable losses, which permanently reduce capacity. The remaining capacities of lithium- and nickel-based batteries after one year of storage at various temperatures are shown in Table 2. Li-ion suffers greater losses when fully charged rather than at a SOC of 40%.
| Temperature | Lead acid at full charge |
Nickel-based at any charge |
Lithium-ion (Li-cobalt) | |
| 40% charge | 100% charge | |||
| 0°C | 97% | 99% | 98% | 94% |
| 25°C | 90% | 97% | 96% | 80% |
| 40°C | 62% | 95% | 85% | 65% |
| 60°C | 38% (after 6 months) |
70% | 75% | 60% (after 3 months) |
Table2: Estimated amount of power a battery can hold after being stored for a year
Elevated temperatures hasten permanent capacity loss. Depending on battery type, lithium-ion is also sensitive to charge levels.
Batteries are frequently exposed to undesirable conditions, such as leaving a mobile phone or camera on the dashboard of a car or in the scorching sun. When using a laptop, the temperature of the battery rises. Sitting at full charge while plugged in reduces battery life. High temperatures also put a strain on lead- and nickel-based batteries.
GeePower Lithium batteries outlast lead-acid batteries by four lifetime.
Thank you for reading about battery storage. If you have more battery-related ideas, please leave a message in the comment area for discussion. If you have any idea of buying lithium-ion batteries in bulk, you are also welcome to inquire about battery solutions and prices. GeePower research and development Team engineers are all doctoral and postgraduate teams from many domestic universities with more than 10 years of lithium battery experience.
