One of the largest barriers for electric vehicle (EV) buyers is charging speed. Nobody wants to hang around a roadside station for 40 minutes. Let’s take a closer look at why EVs take so long to top up, and what is being done to overcome this major hurdle to EV adoption.

The exact time it takes to charge an EV battery will depend on the charging point, the charge left to fill on the EV, and a myriad of environmental factors. For example, a fully depleted Tesla Model 3 with the largest capacity would take eight to 12 hours to charge at home with a high-powered connector. Meanwhile, a Supercharger station could do the same job in 25 to 30 minutes.

One of the habits ingrained in drivers when it comes to fuel is topping up to 100%. With gasoline, this makes sense, but batteries can take significant damage when they’re pushed to those extremes in capacity.

You may have seen features on laptops that prioritize battery health by capping maximum charging at 80%. It’s common practice now for phones to schedule charging rates so they only reach 100% when you’re just about to wake up in the morning — that way, the battery isn’t spending a lot of time bursting at the seams with power.

These precautions have to do with battery chemistry. As we explain in our guide to batteries, they work by moving lithium atoms from one side of a battery to another. The electrons can’t come along for the ride due to a barrier between the two battery halves. So, the electrons take the scenic route through an electrical circuit that powers our devices. Eventually, the electrons reunite with their long-lost lithium buddies on the other side of the battery.

On either side of the battery is a medium where those lithium ions can hang out in the meantime. Those lithium atoms are vital to the structural stability of the mediums they’re staying in. When there’s no lithium at all at either end, those structures take a big hit, which reduces their ability to accommodate lithium ions in the future and ultimately hurts charging capacity. A deep discharge hurts battery life just like an overcharge for the same reason: You’re depriving one side of the battery of the lithium atoms the mediums need to prop up the structure and accommodate more lithium in the future.

Because of the effect these extreme battery charges have on overall life, management systems built into EVs will underreport actual charge at the low end and overreport charge at the high end. This protects users from damaging the long-term health of their batteries for the sake of a little more power in the moment. So even if an EV says it’s at 100%, the battery likely still has some empty buffer that ensures you’re not hurting the long-term battery life.

If you’re charging a mostly depleted battery, the first 80% goes by in about a half hour, while the last 20% takes just as long. As we discussed above, overall battery life is stunted due to overcharging, so charging points will start reducing output when they detect the battery is almost full.

Besides ensuring your EV battery keeps going for the long haul, this slow-down is also a safety measure. When batteries get hotter, they get more explodey. Yes, battery packs have cooling layers woven throughout them, but they’ll only go so far to counteract the heat generated by charging.

Right now, the fastest way for EVs to be charged is at level 3 direct current charging stations. Tesla Superchargers are the big name in that category, but there are other high-speed alternatives.

As battery technology improves, we’re likely to see charging times get better too. Supercapacitors are a promising advancement, allowing vehicles to receive a big charge quickly while making stops. Of course, that hinges on dedicated charging stations being installed along routes. Capacitors also have a much smaller energy capacity than a proper battery, so at most, we’d be looking at hybrid systems.

Graphene is a promising material we’re starting to see in consumer electronics that specializes in fast charging. Scaling that up to EV batteries will provide a seamless improvement in charging times without needing to upgrade infrastructure. Though it will depend on battery replacements, the fundamental battery technology wouldn’t change much beyond swapping in graphene as one of the main components.

Solid-state batteries are a much more dramatic shift in battery technology. These have been a target of research for years, and though they’ve yet to really break through onto the market, the promise is great. Solid-state batteries are light and stable, meaning they would be able to accept a faster charge without the dangers of overheating like we see among traditional batteries with liquid electrolytes.

Hopefully, that explains some of the challenges around charging times for EVs. The waiting is inconvenient, but it keeps batteries working for longer and provides a safety net. In the near future, battery improvements are likely to reduce EV charging times.