What you should know about chargers

Disclaimer: this is not my primary area of expertise so I don't claim to be an expert. I've spent many hours researching the topic and this is what I've found so far.

Chargers are a critical component with respect to lithium ion batteries. Very critical. There are a lot of chargers out there and based on my research, I can only recommend two. The first is the Pila IBC. Bar none, this charger has the best reputation. However, it charges 2 cells at a time and retails for nearly 50 dollars. 

I selected the Xtar MP1 charger because it's high quality.

Only one other charger compares, but it's twice the price and thrice as ugly. 

The second is the Xtar MP1. This is the charger I'll be selling along with my lights. Xtar is a relatively new company but so far their product seems to be top notch. I like the industrial design and this charger has the advantage (unlike the Pila) of being USB based. This means you can plug it into your laptop, use a wall adapter, or even a car adapter for charging. I like this flexibility for a general purpose charger. The MP1 is also a single bay charger and this is great for the more casual user that only owns a few lights. I purchase these directly from the manufacturer and will be selling these chargers separately and as a package deal with my lights. 

If you want to get more technical, read on after the jump. If are a hardcore "input" person you can check out Battery University for tons (and tons) of information.

CHARGE TIME: 

A lot of people ask how long a battery takes to charge. That depends on how deeply the battery is depleted. Also, the MP1 is not a "fast charger," or at least not as fast as some chargers. There are two reasons this is good. First, the charger uses a current of 500mA and this relatively low current makes it possible to charge from a USB port. Second, the AW batteries can be charged with up to 2000mA safely, but charging at high current reduces total battery lifespan.  

The cool thing about the MP1 is that it charges with a USB cable.

So yes, you can use your laptop to charge your light. 

That said, the MP1 should take no more than 4-5 hours to charge a depleted battery. Please note, deeply discharging a li-ion battery also reduces its life span. Unlike other chemistries, li-ion has no "memory effect" so you can charge it any time without loosing capacity. In other words, it's best for battery health to recharge frequently rather than waiting till the battery is "dead." Deep discharge may even damage a battery permanently. If you notice the light dimming you should recharge or install a fresh battery immediately. 

In my personal use, I will put the battery on the charger if I've used it for more than 10-20 minutes. At this level of shallow discharge the battery will top up in 40-80 minutes. 

At the most basic level there are three main features that make a good li-ion charger.

1) Constant current/constant voltage charge algorithm. Without getting into too much detail, li-ion requires a specific charge profile. Many li-ion chargers do not follow this profile, and that fact baffles me. The MP1 utilizes the "correct" CC/CV charge profile.

(EDIT: this issue has been brought into question and is addressed in my follow up "comment" below. I have opted to make this note and leave the original text intact, rather than simply editing the original text.)

2) Accurate ending voltage. Li-ion batteries are not capable of absorbing over charge like some other chemistries. This means it's critical that a li-ion battery never exceed 4.2 volts. The information I've gathered from other users is that the MP1 does a good job of ending the charge at, or below, the maximum allowable voltage. In fact, it errs on the slightly low side...often around 4.1 to 4.15 volts. 

Some power users are bothered by the fact that it doesn't charge really close to 4.2 volts. In my opinion, this is an advantage because you trade a couple of minutes of run time for increased battery life span. The closer you charge a li-ion to it's absolute maximum capacity, the more it degrades the battery's total usable life. 

3) Complete charge termination. This (in my opinion) is the most critical feature for a li-ion charger. This means the charge current is FULLY cut off once the battery is charged. The funny thing is, many generic chargers specifically made for li-ion batteries DO NOT have this feature. They continue to apply a small amount of current even after the battery is full. If you remember...li-ion cannot absorb over charge. Over charge leads to heat build up and if left unchecked may cause the cell fail catastrophically. In other words, catch fire. 

Woah! Okay I know you might suddenly be thinking li-ion batteries are dangerous. Keep in mind that virtually every modern laptop and cell phone uses li-ion batteries...and this is why having a high quality charger (and batteries) is very important. This is also the reason I won't sell anything but Xtar chargers and AW batteries.