Charging overnight isn't necessarily a bad habit, and is really no different than charging any other time, if you are charging for a similar length of time or charging to 100% of capacity. What makes charging overnight a potentially less than appealing practice is complicated but I'll try to explain in a concise manner, though there are enough threads from me and others here to give you the long and short of it if you wish.
Originally Posted by GSdub510
Charging ANY TIME with the power ON can create a confusion for the charger's metering system which is trying to determine when the battery has reached "100% of capacity", signaling an automated shut down of the charging to prevent overcharging. Due to what is known as a "parasitic load" (the phone using power while the battery is vying for it as well), it can "perceive" that it's reached full capacity - due to a miss-read of battery voltage (the measure that identifies the level of charge), when it's much less than 100% of capacity, and so interrupt the charging process too soon.
I say 100% of capacity rather than "full" because full can be mistaken to imply the same amount each time, like "filling a glass of water", where the glass will always hold the same amount and so full is full. Batteries are a different animal. A battery has a maximum "safe" charge capacity, which starts out high from the factory, but over time and multiple hundreds of charge cycles gets smaller and smaller, until eventually the battery will only hold a much smaller portion of what it used to hold (end of life for these batteries is between 80% and 90% of what the specified capacity was when new).
The reasons why are many, but what's important to understand is that 100% of capacity for a new battery, versus 100% capacity for a battery that's 1 year old, versus 2 versus old, or one that's been charged 10 times versus 100 times versus one that's been charged 400 times, will all yield different "capacities".
It's sort of like a glass that shrinks both each day even without use, and also shrinks each time you use it. Even though the glass is smaller each new fill, if you fill it to the top each time, you are still filling it to 100% of capacity each, but its capacity is less later in its usable life. If the glass has shrunken by 20% (like a battery that's perhaps 1.5 to 2 years old or has been full cycle charged 500 times), and you fill it to the rim, it's once again 100% full, but its capacity is only 80% of what it was originally.
Imagine you and a friend decide in a pact to go shopping, and you both agree that you are each going to spend 100% of what's in your pockets at the store. Now imagine that your friend comes to the shopping spree with $100, and you bring only $80 (not much of a shopping spree, I know, but humor me for a moment). Once your shopping spree is over and you are both flat broke, your friend will have spent 100% of his or her $100, while you will have spent 100% of your $80. You both spent 100% of what you brought in your pockets, even though you had 20% less money to start. You see, 100% of anything, even zero, is still 100%.
Now, charging these specific types of batteries to 100% capacity (no matter whether it's new, 1 year old or 3 years old) actually reduces the lifespan (aging) of the battery by accelerating the "shrinking" of capacity. It's because the most stressful portion of a charge for these batteries happens at the top of the charging cycle (the last 90% to 100%). Also, the longer the battery remains at 100% of capacity, the faster it ages.
Charging fast (with higher current, or higher maximum voltage such as other third party chargers) generates excess heat which is also detrimental to a battery's lifespan. In contrast, charging in shorter charge cycles, for instance from 25% to 75% versus 15% to 100%, and also charging in the lower portion of the range (15% to 90%), will result in a battery that will take many more charges over its lifespan and will result in a greater total amount of stored power supplied by the battery over the same timeframe.
Now, the real question is, how long does the battery have to last YOU! If you are going to replace your phone with an upgrade in a year or so, then any minor shortening of lifespan caused by charging every night and leaving it on charge while you sleep over the next year or so should be of little concern for you. On the other hand, if you're the kind who will have this phone for the next 3 or 4 years, then charging overnight to 100% every time would be something you should try to avoid. There have been a couple heated discussions about this and my recommendations, yet scientific testing by expert battery companies proves this irrefutably.
The bottom line is, if you only use 40% - 60% of the power each day (like from 80% down to 40% or 20% such as with the RAZR MAXX), and you charge every night, your battery will last longer than someone who uses from 70% to upwards of 85% - or worse 100% of the power each day (like from 100% down 30% or lower) and charges every night. How much of a full charge you use each time is known as "Depth of Discharge" (DoD).
Further still, if you use only 40% - 60% each day, but charge in those shorter burst charges I mentioned throughout the day such as while in the car, or at the office PC (meaning your battery never really gets charged to 100%), rather than plugging in when you go to bed and letting it sit on the charger for 8-10 hours overnight, your battery will last longer as well. These batteries actually prefer to be charged with multiple partial charges rather than to be charged once in a full charge to 100%, and they can last up to 2-3 times longer if charged in that manner.
Whether it's practical for your lifestyle or routine to charge in such shorter bursts in the middle of the day or evening, rather than simply making it part of your nighttime routine is a question only you can answer. Whether you need it to last you 1-2 years or 3-4 years is also something only you can determine.
Also a side-note, try to avoid allowing the battery to ever discharge to 0% and automatically power down. Instead, power it down well before it reaches 0% (like at 15%), and charge as soon as possible afterwards. Just like charging to 100% is stressful to the battery, discharging to below 15% also has a diminishing effect on battery life. Also pushing the battery into a deep discharge (near or to 0%), can result in a situation where it then may not respond to the charger to accept a charge again and cause bootlooping and other failed boot consequences.
There is one thing you should practice no matter what your charging routine, except if you are using it from 100% to 15% on a frequent basis, and you charge with power off to 100%, and that's to do a 3-step "meter training" charge about every 2-3 months. It goes like this;
The next time you will not be using the phone for at least 3-5 hours (3 for the RAZR, 5 for the MAXX)...
Step 1) Power it off by pressing and holding the Power button, then selecting "Power off" from the menu.
Step 2) Plug in the Motorola Stock charger and Stock Power Cable, and allow it to self-start into "Charge Only" mode.
(you'll first see the familiar red M logo, then followed by a large animated battery icon with a "liquid" level and percentage of charge in numbers). Allow it to charge in that mode for the next 3-5 hours (longer is OK, but you MUST let it reach 100%). To see what level of charge it is at any time along the way, press and release one of the volume buttons. In a few seconds you'll see the animated battery again. Let it timeout after about 10 seconds and it will resume charging.Step 3) Once it has reached 100% charge, you may remove it from the charger and power it up normally.
Now feel free to use it as you would over the next day or so, but don't place it back on charge until it has reached 15% and the phone signals "Low battery" with a screen warning and "Bong" sound.Step 4) Once it reaches 15%, repeat steps 1 and 2 just one more time. Afterwards, you can power and charge in your normal routine until the next "training" charge in a couple months.
This "training" is done to keep the Meter and Charging system calibrated to the battery's actual and decreasing capacity over time, so when it displays 100%, it will be representing the maximum charge that the battery can safely handle at that time. Out of calibration metering can result either a lesser charge level (which would result in an apparent shorter power cycle - thinking "the battery is dying quickly"), or a higher and potentially damaging charge level. Under nearly all normal circumstances charging beyond what the battery can safely handle is not a concern since the charger is designed to prevent overcharging. However, there are some who suggest a bad practice called "bump charging" which can do considerable damage to the battery, shortening its lifespan and potentially putting it at a voltage level that could result in it self-destructing in a potentially violent end of life suicide.
Finally, charging with the power on, versus charging with power off will potentially result in considerably different charge levels. Charging with power off is the only SURE way to charge to 100% of the battery's capacity at any time. Charging with power on (as most do), can result in the phone displaying 100% charge when it's actually only charged to as much as 90%, or even considerably less.
So if you feel your phone is "dying too soon during the day", try a full "saturation" charge to 100% with the power off and see if it doesn't last considerably longer the next day. Also, feel free to use the battery to a 15% discharge level. If this results in a longer days' use, it's time to do a "training" charge cycle again.
I recommend the only times you charge to 100% with power off are when you are doing the training, or when you absolutely need the most run-time that the battery can provide for you during a day, because you are going to be away from any external power sources.
I've seen some mention taking these phones camping and questioning how to make it last through the multiple day excursions. Well, I gotta say it's not going to last if you leave it powered on constantly, and if you do ANYTHING other than make an infrequent phone call while powered on. It's not your old flip phone that could have done that while remaining powered on for the several days straight.
If you plan on being away from any typical power source, such as a wall outlet, car adapter or computer for more than a day, I recommend you invest in a portable power booster. There are plenty that can give you multiple charges and aren't all that much bigger than a wallet or pack of cigarettes.