Charging your PHEV to 100%? It’s Not What You Think

Charging your PHEV to 100%? It’s not what you think!

PHEVs are a type of hybrid vehicle but, unlike standard hybrid vehicles, PHEVs are geared heavier on the electric side and lighter on the internal combustion engine.

Fortunately, it’s less complicated than a regular EV and a combustion engine, even though you are technically getting two.

As far as charging it to 100%, plug-in hybrids feature a battery management system that keeps you from being able to charge it to 100%. This provides protection from both undercharging and allowing a full depletion of battery charge. 

Basically, the battery management system in a PHEV (Plug-In Hybrid) restricts a portion of the battery from being accessible by the charging station or your at-home charger.

It can only charge 90% and, as far as the charger is concerned, once it hits 90%, it’s at 100%.

How PHEV’s Work

The vast majority of the charge your PHEV gets is going to come from the internal combustion engine. As the car runs on gasoline, it slowly charges up the battery in your vehicle. 

When you plug it in to charge at night, the battery cuts it off at 90%, which avoids overcharging or charging the battery to maximum capacity.

The remaining 10% is completely negligible because your vehicle’s engine will be more than enough to make up for the missing charge. 

We say 90% but, depending on the make and model of your PHEV, it might be 80% or 85%.

Regardless, these vehicles do not technically reach 100% charge, even though it may reflect that your battery is fully charged on your dash display. 

Most PHEV vehicles are not designed to carry the load very far on battery power alone.

For instance, the Chevy Volt plug-in hybrid is designed to only go 40 miles on a full charge, which is basically 90% plus whatever is gained from the internal combustion engine. 

The battery is heavier than a traditional hybrid but it’s nowhere near the kind of battery you get in an all-electric vehicle.

Standard hybrids don’t plug in and charge at all. The entire charging mechanism in a hybrid comes from the work of the combustion engine. 

Why a 100% Charge Degrades the Battery

Any battery that’s rechargeable has a limited number of cycles, meaning that after a set amount of charges from 0% to 100%, the battery’s overall capacity to hold a 100% charge is reduced.

That means the efficiency of the battery is reduced and it’s only downhill from there. 

The truth is, rechargeable batteries manufactured today don’t allow themselves to hit 100% or 0% to avoid rapid degeneration.

It only looks like you have a 100% charge because that’s what the system is designed to reflect when the battery is at 90%.

The problem with batteries reaching 100% charge is that there are a number of factors at that level that cause problems.

Your battery can recover from these problems but it’s like breaking the same arm over and over again.

Each time it heals, it’s not the same productive arm that it was before.

Lithium-ion batteries are the types of batteries you find in EVs, PHEVs, smartphones, and laptops. Every time you charge the battery, lithium ions are pulled from one layer (lithium cobalt oxide) into another layer (graphite).

When the ions are pulled from the graphite layer in this way, it produces energy. As the battery is used, the lithium ions return back to the cobalt oxide layer gradually.

When you charge the battery to 100%, you’re essentially transferring too many lithium ions and the result is instability. 

It does damage. It might be damage that you can’t see right now but it’s damage all the same—like microscopic tears over time.

The more tears there are in the overall material, the less stable and supportive the material becomes. 

Manufacturers have overcome this problem by creating and installing battery management systems that won’t allow the shifting of too many lithium ions into the graphite layer at once.

This keeps the battery from becoming unstable and damaged over time. 

Does This Mean You Can Charge Your PHEV Overnight?

That’s exactly what it means. You can leave it on the charger all night and the battery management system will halt the charging process once it reaches a certain percentage of charge. This might happen at one o’clock in the morning.

If you wake up at 6 o’clock in the morning, your car will still be sitting at the exact charge that it reached at one.

This design concept isn’t just for PHEVs or EVs. Apple, Samsung, Google, and other smartphone manufacturers, along with PC and laptop manufacturers, use the same technology. 

The point is to keep your iPhone, Android, laptop, or PC battery from overcharging or even reaching 100%. It doesn’t matter what lithium-ion battery it is or in what device it’s being used. 

How Often Do PHEVs Need to Be Charged?

As long as there is gasoline in the vehicle, you never have to charge a PHEV.

When the battery in a PHEV reaches a certain discharge percentage, the internal combustion Engine starts charging it again. 

On its own, on a long trip, for instance, the gasoline engine will effectively charge your PHEV back to its normal capacity.

You don’t have to do anything. If you take short trips to work every day, like a 10-mile round trip, you can charge it nightly and never use the combustion engine. 

Part of the advantage of owning a PHEV is that you can use either or.

\Unlike a hybrid, which can only use a combustion engine that’s supported by a battery, you can drive a PHEV on the battery alone, at least for limited distances.

Or, you can use your gas. It’s entirely up to you how often you charge it. 

All Things Considered

Whether or not you “should” charge your EV to 100% is pretty irrelevant because you simply can’t.

The battery management systems inside PHEVs and EVs today won’t allow you to charge it to 100%.

If you weren’t aware of the battery management system, you probably only assumed you were charging it to 100%, to begin with.