13. Why do new batteries become useless
after some days?
Answers
Explanation:
potential difference btw 2 terminals become 0
Answer:
This depends on the type of battery
Explanation:
Let's look at some of the more common ones:
Primary (non-rechargeable) batteries, like all batteries, will slowly lose charge over time. However, after four years, most name-brand disposable alkaline batteries will probably still have most of their original charge. Lithium-based primary batteries will probably last longer than alkaline batteries. Since primary batteries can't be recharged, any self-discharge is permanent. Most disposable batteries have an expiration date printed on the packaging.
Lead-acid batteries lose charge at a rate of about 2-8% per month at 20°C; the self-discharge rate approximately doubles for every 10°C increase in temperature. After four years (48 months) at 20°C, if the battery has never been recharged, it will only have about 10% of its original charge left (at most 40%). Sitting at a partially-discharged state for this long will probably have permanently damaged the battery through various mechanisms, including the formation of non-conductive lead sulfate on the plates. Flooded lead-acid batteries will lose water by evaporation as well, so in addition to charging the battery periodically during storage, water will need to be added. If this maintenance is done regularly (at least every 6 months is probably a good rule of thumb), the battery will be in good condition after four years, although it may have lost some capacity compared to when it was brand new.
Nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) batteries lose charge quickly (20% per month, although newer designs have reduced this to about 2-3%) but are not harmed by storage in a discharged state; the only danger is that they will eventually lose electrolyte through evaporation, but this will take a long time since they are sealed. If a multi-cell nickel-based battery is stored with an electrical load attached, it is also likely that one or more cells will reverse polarity, which causes permanent damage. But if the unused battery is not connected to anything, it will probably be fine after four years if it is fully discharged and then recharged after storage.
Lithium-ion batteries have a low self-discharge rate, so it's possible that a battery stored for four years will still be fine. However, they do degrade over time, especially if stored fully charged, so there will probably be some capacity loss. Some batteries have built-in monitoring circuitry that consumes charge and results in a higher overall "self-discharge" rate, and if the battery is deeply discharged it may be permanently damaged. Usually it's recommended to store lithium-ion batteries at about 40-50% state of charge to reduce the rate of degradation while still leaving some room for self-discharge.
In all batteries, storage at low temperature will improve shelf life. However, manufacturers generally don't recommend storing batteries in the refrigerator, mainly because condensation can form on the battery when it is removed from the fridge. If the battery gets wet during storage, obviously the rate of discharge will be increased since the wet surface of the battery can form a conductive path between the terminals. Freezing can also damage water-based batteries (all but lithium-ion) due to expansion of the electrolyte.