Batteries lose their power within 1 to 2 hrs so make sure you bring along spares if you are spending the night trekking or hunting durians in Ubin. Disposable batteries are expensive and rechargeables are the way to go.
For rechargeable AA/AAA cells, my favorite is Sanyo Eneloop brand. These batteries do not drain down while unused compared other common NIMH rechargeable batteries. Mustafa Centre prices are very competitive compared to many retail shops.
New improved Sanyo eneloop batteries
Although users may not notice the difference, the improved Sanyo eneloop promises better all round performance. Click on Sanyo product page to find out how to distinguish new ones from the old.
You need a charger too. I prefer to use cheaper slow 8 hrs charger. They prolong battery life as they are cooler and safe even if you leave the batteries charged for weeks or even months.
Not so with quick 1 hour chargers. The batteries get hot while it is being charged and get really hot when its near full. The charger’s circuitry detects this and switch to 200mA trickle charge. That depends on QC which is questionable for most cheap China made knock-offs. Have a bucket of sand ready if it catches fire.
The next step up are disposable CR123A Lithium batteries which Surefire flashlights use. These batteries carry up to 3 volts with its multiplier effect of 6 or 9 volts in series. They can last unused for up to 10 years and do not leak battery acids compared to alkalines, the common cause for flashlight failures. They are expensive but you can buy them in bulk at Sheares Technologies. Some camera shops will sell you in box of 10 for $2.80 each. Try Max Photo at Pagoda Street. Its not advisable to mail order them as it may be held at customs due to higher risks of fires if packed poorly. CR123A batteries cannot be recharged.
Many new flashlights allow the option of using rechargeable li-ion batteries. Unlike ordinary NIMH rechargeable batteries, they self drain slowly when stored unused. These batteries run at higher voltage at 3.7volts with higher current draw. The benefits are higher power in a smaller package or both power and longer runtime with larger batteries. Read your flashlight manual to see if such batteries can be used as the wrong match will result in burn out bulb or reduced LED life. The positive end (+) of the battery has to be inserted correctly also.
They are less safe if used in series and knowledgeable handling is needed to prevent small explosions or fires. Please visit candlepowerforums and take your time to read its faq.
You will need to know important details like different cells sizes, their capacity differences, protected or unprotected, current drain.
Cells size are given in 5 digit number schemes. The first 2 number prefix indicate battery width and last 3 number suffix indicates battery length. A 18650 battery is therefore 18mm wide and 650mm long, about twice the length of R123 or 16340 cell.
Larger capacity means longer runtimes. But cell capacity are mostly over optimistic so don’t fall for manufacturer claims.
Protected cells have built-in circuits to prevent dangerous over discharge or excessive current drain. The term tend to be loosely used so buy from reputable manufacturers (hard to do since most batteries are made in China). Look for cells with vent holes which help release pressure if the temperature rises and gas expands.
Discard any cells that shows signs of leaking or cracks if dropped as they can be fire hazards. Promptly recharge any drained cells to at least 3.7volts to avoid permanent damage. Keeping the battery unused for prolong period at full charge of above 4.1 volts reduces its normal life span.
Finally, the cell positive end may be button or flat top, an important distinction as some flashlights contacts only work with button top cells.
As li-ion cells are more expensive, choose flashlights that share common battery sizes such as 18650 size.
AW li-ions in different sizes
You may order online through a HK online dealer or through dealextreme. Again, read reader reviews and users recommendations before you purchase such batteries and chargers dedicated for them.
Li-ion batteries by AW are very popular among flashlights enthusiasts. They can also be ordered from Lumen factory with fast shipping from Hong Kong. Order the black colored ones. The orange ones need careful handling due to its high current draw. AW 18650 3100mAh is highly recommended. Although more expensive they run longer.
Other than online orders placed with Hong Kong or China which ship via Hongkong Post, never ever place your battery orders with shipping via Singapore vPOST. vPOST is a useful service for magazine subscriptions, ebay shipments containing garments or ladies handbags from USA for retailers including Amazon who do not offer international shipping. The US Federal Aviation Administration issues guidelines that batteries must be properly packed for transportation. vPost go to the extreme by refusing acceptance of anything containing batteries including those of safe chemistry including alkalines and NIMH. They even go to the extent of refusing to accept if they believe there are batteries when there aren’t any. Your orders will be stuck in some US post office for rejected delivery waiting to be claimed. So spare yourselves the hassle and do not tell your ebay seller to ship to your Vpost USA address, be it flashlights, laptops or mobile as nearly every electronic equipment that are now battery powered.
The nimh chargers I am using now include Lacrosse BC-900 which seems to be reliable so far. My experience with Maha chargers is mixed (read cheap parts).
As for li-ion cells, I like to know what is happening so I bought an expensive Triton hobby charger. You can find many expensive sets at RC (radio control toys) shops concentrated at Fook Hai Building. I am now testing the icharger 106B+ which allows PC monitoring. This unit was ordered online from Hobbyking. Their service is fast with affordable express shipping.
Update: 20 May 2010. The icharger 106B+ failed to work and I have to send it back. It took more than a month and plenty of hassle to get a replacement. Online orders are full of such pitfalls. Other than that it is a well featured charger and am very pleased with it.
There are plenty of China made chargers for li-ion cells which are cheap but reliability is a big question mark. Some of them keep charging until voltage hit as high as 4.3 volts before termination. Runaway charging may even cause flaming and explosion. Li-ion chargers should have “constant-current, constant-voltage (CC/CV) circuit”, meaning it will charge at the highest user selected current before it trickles down, keeping within safe voltage of 4.2 volts and terminating once it reaches that.
Beside full featured hobby chargers above, other cheaper recommended chargers include 4Sevens smart charger.
“World’s smallest” Li-ion charger custom made by Cottonpickers
A multi-meter is best for measuring remaining capacity of your li-on cells. It should not be above 4.2 volts when charging is complete while sagging down to 4.1 volts after a day. Li-ions should be recharged promptly after use especially if it is empty at 3.6 volts or below to prolong their life spans.
4.2V = 100%
4.1V = about 90%
4.0V = about 80%
3.9V = about 60%
3.8V = about 40%
3.7V = about 20% (for long term storage)
3.6V = empty
<3.5V = over-discharged
DealExtreme multimeters are cheap and popular among on-line buyers sku #619 and sku 9636.