This week a reader asks two specific questions about charging batteries.

1. Are faster chargers harder on batteries than slower chargers (for example, is a 20-watt charger harder on a battery than a 12-watt charger)?

2. Are more partial charging sessions (for example, to only 50%) harder on a battery than fewer charging sessions to 80%? Is it, for example, hard on a battery that’s at 35% capacity to recharge it to only 60%, resulting in more charging sessions than waiting for the battery to drop to 20% before charging it to 80%? Are those partial charges hard on the life of the battery? Would a battery always kept between 20% and 80% last longer than a battery more frequently charged between 30% and 60%? Is there an advantage in waiting to 20% before charging?

Wow, this is a quite detailed query, and I like it.

To answer the first question, faster chargers (that provide more power) are indeed harder on your battery than slower chargers.

Faster charging produces more heat, and heat will cause your battery to degrade faster. How much faster is a moving target. Every battery is different and everyone’s charging habits will be different.

The second question is also great. I love that people take the time to ponder the details of charging to specific ranges. Some might call this overthinking, but I appreciate it.

The fact is that today’s rechargeable batteries don’t love it when they are fully charged or run down too close to empty. The sweet spot (remember that phrase) for battery longevity is to keep their charge level between 20% and 80% for as long as possible. In fact, most phones will let you optimize charging by delaying the charge past 80% until just before you need it.

We are generally creatures of habit, and your phone will, over a bit of time, figure out your charging patterns. Say you put your phone on the charger every night at 10 p.m. With optimized charging, your phone will charge up the battery to 80% and keep it there. Then, an hour or so before you wake up, it’ll charge it up to 100%. I think most of us would benefit from having optimized charging turned on. Look in your phone’s settings under Battery.

In my opinion, there isn’t much measurable difference keeping a battery charged between 30% and 60% or 20% and 80%.

If you keep the charge level in that sweet spot, it will be best for the longevity of the battery. More frequent and smaller charges won’t really have much to do with shortening the battery life.

But, in the end, will all this attention to keeping the battery charge in a specific range really make much difference?

Maybe, but it really depends on how long you intend to keep your phone.

Rechargeable batteries don’t just stop working. They just lose their capacity.

Their degradation is gradual. After two years, a healthy battery (one that you’ve taken care to keep between 20% and 80% as much as possible), might still have 90% of its capacity remaining.

On the other hand, if you don’t pay attention and charge up to 100% every night and drain the battery down to zero every day, after two years your battery might have 70 or 75% of its capacity remaining.

Is that a noticeable difference? Sure. For a heavy user, it’ll mean you run out of battery earlier in the day.

I certainly understand wanting to get the most life out of your battery, but many of us will likely replace our phones right around the time we notice the battery life not meeting our needs.

If you really want to keep your phone, you can always replace the battery after a few years. A replacement will cost you -- at most -- about $100.

I’ll leave it up to you to determine if years of worrying over the phone’s battery level is worth the cost of a replacement battery.

That said, I personally don’t like to let my phone’s battery get below 20%, but it happens occasionally. I charge overnight and I do have optimized charging turned on.

I usually keep my phones about three years before getting a new one, and I have yet to need a replacement battery.

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