If you charge a tablet or an EV battery pack for your power drill to 100% but do not use it for a few months, they will be dead the next time you pull it out. What’s going on. Why can’t batteries stay charged ?
Energy does not want to stay in one location; it prefers to move in order to achieve equilibrium. The electrical energy we store in batteries is analogous to a swarm of schoolchildren crammed into a classroom. The kids squirm around, full of energy, hoping they could be outside the school, running around the playground.
The electrons stored in the battery are like fidgety toddlers, yearning to be free and bouncing around again. The chemical process within a charged battery continues even when the device is switched off or they are unplugged, but in a much more muted manner than when they are in use.
This constant low-level operation gradually depletes the stored energy. It’s known as self-discharge—electrical discharge that occurs while the battery is not subjected to an external load—and it’s inescapable.
While all batteries self-discharge as a result of their design and, you know, obeying the physical laws that govern the universe, the pace at which they drain varies greatly. Here are some common rechargeable battery types and how quickly they discharge.
| Battery Type | Self-Discharge Rate Per Month |
| Lithium-Ion | 2-3% |
| Nickel-Metal Hydride (NiMH) | 25-30% |
| Low-Discharge Nickel-Metal Hydride | 0.25-0.50% |
| Nickel-Cadmium (Ni-Cad) | 15-20% |
| Lead-Acid | 4-6% |
You can’t completely prevent batteries from draining, but you can reduce the discharge rate by doing one easy thing across all battery types: keep them cold.
Of course,cool them within reason. Do not freeze your batteries (condensation difficulties while bringing them in and out of the freezer can create major problems for the complex internal circuitry present in current rechargeable batteries), but do everything you can to minimize heat.
Even with the finest care, batteries deteriorate with time, and if a battery is no longer adequately holding a charge, it should be recycled and replaced.
Reference- How-To Geek article, Inside EVs, EV Obsession, Popular Mechanics