What causes a lithium battery to only partially charge

There's no harm in keeping it on charge all the time. Unlike older rechargeables, newer Li-ion batteries don't need to be broken in by running them down and then recharging.

Try fully discharging the battery first and let it sit for a few days. Then fully recharge before use. What happens with battery operated drills is the batteries develop what is called memory of the charge level when they are recharged and will not charge past that point but the charge light will show full charge. It happens when the drill is used for a period of time and then the battery is placed in the charger ready for next time instead of using the drill until it is flat or leaving a partially used drill on the bench and not recharging it until it is flat

If the recharageable battery is more than 3 - 4 years old then the battery could be worn out.Rechargeable batteries have a finite number of charge and discharge cycles andwill lose their charge capacity over time, i.e. won't charge to 100% andgradually the charge reduces until the battery won't charge up at all. OR Thebattery shows a 100% charge but when the adapter is disconnected the batterydrops off to zero capacity in a very short time. If the battery drops to anunacceptable charge level then the battery needs to be replaced.

Do not try this since the charging circuit for lithium batteries are different than nicad! Improper charging of lithum batteries can cause a fire.

How long have these 2 batteries been standing idle without being charged? Lithium ion batteries can still discharge if left for too long. There is a voltage detector which detects whether the cells are too far discharged to be safely charged again and if that occurs the circuit is broken and the batteries will be deffective in the charger.
I have had the same problem with these and other LI batteries. Answer is replace the batteries and then make sure they are given a quick charge on a regular basis. However common advice seems to be that LI's should not be kept fully charged, but just partially charged until needed, then charge them for use, especially if usage is sporadic

Rechargeable batteries do not last forever. Probably need new battery. LED flicker could be from low battery voltage or bad connection.

How long have you been doing this for (months)? You may have already drastically reduced the life of your battery

Battery & Charging

The Zen’s battery:

The Zen uses a 3.7v rated Lithium-Ion rechargeable battery. A 3.7v rated Lithium-ion battery actually gets charged to around 4.2v with a tolerance of +/- .05v. A charge of 3.7v/3.8v is actually about a 50% SoC. At 3.3v, lithium-ion batteries have typically only utilized 70% of its 100% charge capacity.

Charging Voltage = 4.2v (4.1v)
Nominal Open-Circuit Voltage = 3.7v (3.6v)

A note on Over-Discharging and Over-Charging:

In general, Lithium-Ion batteries do not like to be overcharged (usually above 4.2v) or excessively discharged (under 2.5v-3.0v). If a Lith-ion battery falls below 1.5v, then typically you shouldn't try to recharge it at all for "safety" concerns. A fully discharged lithium-ion battery causes the formation of copper shunt in the cell which begins to get extremely hot when attempting to recharge. A lithium-ion battery should not be charged above 4.3 volts. Above 4.3 volts and the cell causes lithium metal plating on the anode. The cathode material becomes an oxidizing agent and loses stability and begins releases oxygen. This can cause the battery to heat up. Lithium-ion cells should never get above 130°C (265°F). At 150°C (302°F) the cell becomes thermally unstable and can eventually lead to a thermal runaway. These are the safety reasons why the low and high voltage cut-off and temperature sensing circuits are used. If the internal temperature of the battery gets to high, the temperature sensing circuit can initiate a mechanical pressure switch that will permanently cut-off the current path and prevent anymore charging.

How do you charge the Zen (Battery)?

It can be charged by connecting it to a USB port on a computer or by using an AC Wall Charger within the Zen's charging specs (see below).

Can I use my cell phone's AC Charger to charge my Zen?

I believe the max input voltage of the Zen is around 5v. Most devices that can charge or run off the USB host power can handle the max 5v of USB ports. 4.2 volts is usually the max Lithium ion batteries are charged to. It is usually around when the high voltage circuit is triggered and stops the charging of the battery. I would not connect a charger to the Zen that puts out more volts then 5v with an output current beyond 2400mA (2.4A) to be safe.

When and how often to charge?

To be safe, I would avoid frequent full discharges because this puts additional strain on the battery and usually shortens its life. Partial discharges with frequent recharges are better than one deep one. Recharging a partially charged lithium-ion does not cause harm because there is no "memory effect" like with older type Ni-Cd (nickel-cadmium) batteries.

Do I need to charge the Zen for hours before I use it for the first time?

With Lith-Ion batteries, the first charge isn't any different then any other charge. There is no technical need to fully charge it the first time you get it other then the fact of being able to use it longer since it will have a full charge. They are not like other types of previously used rechargeable batteries that needed the full charge at first. Most likely by the time you get everything all figured out and loaded onto the device, the battery would be fully charged anyway.

Please note: I do recommend that you at least connect the Zen to a computer while it has sufficient charge on the battery in order to properly be detected and have its devices drivers load properly. In other words, don't use your new Zen for a period of time to where you drain enough power from the battery to just come on and turn off automatically or to the point the Zen doesn't come on at all. If you do, then you may have detection and charging issues when you go to connect the Zen to the computer.

How long will the battery in the Zen last?

Lithium-Ion batteries have a life span of about 300-500 discharge/charge cycles or 2-3 years from being manufactured.

Storing or not using the Zen for long periods of time:

Lithium-ion batteries (by themselves) with no built-in voltage monitoring circuit have a really low self-discharge rate (1-2% a month) when not being used. Having the addition of voltage monitoring circuits will slightly increase the discharge rate, but should not reach the point of excessively discharging the battery to where it won't turn back on unless sitting unused for an extended period of time and if its last state before powering off was a already in a low voltage state. So, as long as you aren't storing it for long periods of time at a low discharged voltage, the battery should be ok to recharge.

Accidently left the Zen plugged into the Computer all night or for a long period of time:

I wouldn’t make a habit of doing so. Long term usage like that could shorten the life of the battery. Although you may be fine for a while, leaving it plugged in occasionally all day and night, most likely won't hurt it, but leaving it plugged in every day and night may not be a good idea. Although once it is charged to 100%, the battery's internal high voltage cut-off circuit should keep the battery from over-charging and the devices charging circuit should keep applying a trickle charge when detected a drop in charge below full. However, keeping a Lithium-ion battery plugged in and fully charged keeps the battery's temperature elevated. Exposure to prolonged elevated temperatures can cause capacity loss which can then cause the battery to no longer be able to charge or hold a charge. Plus, it may be a small chance, but there is a chance that exposure to this condition for long periods could also increase the chance of a circuit failure (charging, high voltage, temperature sensing) and allow for a severe over-charge to take place to the point of thermal runaway which has been known to cause the occasional "exploding" battery, but in most cases just melt (and take some of the device with it) or catch fire.

A note regarding USB and charging:

Per the USB specs:
USB 1.1 = Minimum supply voltage is 4.4v
USB 2.0 = Minimum supply voltage is 4.75v
Both maximum supply voltages are 5.25v and a current of 500mA.

Before the USB bus interface can begin charging a device (Zen), it must return a device identifier to the hub driver (or device driver). Once the hub driver has the returned information from the device (like power requirements, supported transfer speeds, etc.), it can then begin charging the device based on those retuned values. This process is called Enumeration. Until enumeration has completed, it may not draw more than 100mA from the bus. Once enumeration has completed, it can then begin drawing up to the 500mA allowed by the USB bus.

No. Lithium Ion batteries prefer a partial rather than a full discharge. Repeated full discharging robs the battery of its capacity (useful life), the Lithium Ion battery prefers shallow over repetitive deep discharge cycles. Besides cycling, the performance of the Li-ion is also affected by aging. Capacity loss through aging is independent of use however the capacity is affected by both aging and usage. Battery wear-down on lithium-based batteries is caused by two activities: actual usage or cycling and aging. The wear-down affects by usage and aging apply to all batteries but this is more pronounced on lithium-based systems. The Li-ion batteries prefer a shallow discharge. Partial discharges produce less wear than a full discharge and the capacity loss per cycle is reduced. Simple Guidelines to extend useful life of the battery Charge the Li-ion often, except before a long storage. Avoid repeated deep discharges. Keep the Li-ion battery cool. Prevent storage in a hot car. Never freeze a battery.

The Lithium batteries that are provided with the camera will supply approximately 200 images. The Ni-MH batteries will provide approximate 100 shots per charge. The B-10LPB Lithium Polymer battery will allow 500 - 700 shots per charge and can be recharged approximately 500 times. B-12LPB Lithium Polymer Battery will deliver twice the power allowing 1000- 1400 shots per charge and can be recharged approximately 500 times. The Alkaline batteries, although can be used, is not recommended due to very low battery life.