Old NiMH Vented, unable to sustain high current

This post is just for info, and for anyone who is interested.

I had some old NiMH batteries that came with a digital camera. NiMH, with vents, 1700mah, came with Olympid Camedia camera. After reviving them with my BC-700 (the dummed down version of the BC-900 with almost the same features), they returned from ~900mah to 1700+ mah (1710 to 1780 mah, discharging at 250ma). I was very surprised that they still held above its rated capacity! I had some other "Digital" branded batteries. About 60% were dead, and the rest were about 400-100 mah (out of rated 2000mah).

Basically, I thought these Olympid Camedia 1700mah batteries were still good. To give it a real runtime test, I put them into my Fenix L2D CE, and ran it on turbo. About 23 minutes later (had a timer running) I looked and notice the beam was definitely not turbo. Grabbed the flashlight (it was warm, not too hot) and wow! the endcap was like a balloon. Instantly twisted off the tail to release the gas (didn't smell anything)... realized that these batteries could not sustain such high currents.

So then I put in the second pair (camera uses 4 batteries, so I had 4 batteries to test). Within 8 minutes, I could see it start to bulge... and the beam started to dim (though not to the low mode... which the first set did).

In conclusion, old NiMH batteries probably have built up internal resistance, and therefore cannot sustain long periods of high current, and ... vent.

... off to recycling they go!

Now I'm testing some Digipower 2700mah batteries (looks like a cheap brand). I charged them to full (2140mah) about two weeks ago. Before testing, I stuck them into my BC 700 charger and they read 1.15 V (meaning not full).

After charging, I tested in L2D. Able to sustain turbo mode without any problems.

However, when I was charging them (since it read 1.15v) at 700ma, one charged normally (climbed up to 1.49V), while the other's voltage never went above 1.21v (stayed there for a long time). Accumulated charge was about 2000mah, but the voltage was abnormal. The cell was not hot, and I knew something was wrong (either the battery, or the charger). Took it out of its slot, put it back in, and charged it at 500ma... the voltage started to go up normally (I don't think it was the difference in current... maybe something else).

removed for the time, until i do a retest

Many accounts here on CPF re rubber tailcap covers expanding with Fenix lights. Even with Eneloops.

Bill

just notes:
tiny lights that go into extreeme turbo modes and output much and much light like 180+lum type light, are highly dependant on the users hand leeching off some of the heat of the body of the flashlight.
i always mention NOT to leave a small hard running light alone on the table there to do a runtime, many of them will get to hot for the led, and damage the led.

it could be the increased temperatures via the led and the driver , pushed the battery over sooner than just the load draw on the battery would have.

Go for a walk best way to test a small light on high power settings, good for you, good for the led, good for the battery.

VidPro said:

Go for a walk best way to test a small light on high power settings, good for you, good for the led, good for the battery.

Click to expand...

No, no, you drop it in a bucket of water, to test runtime and waterproofness together

also non-LSD NiMH that have been sitting a long while need a few (3-5) cycles of lo to moderate discharge to limber up b4 going full turbo.

myabe they're just not hi-rate cells.
batteries that come pre-packaged with an electronic product tend to be the cheapest the manufacturer can source.
do u know fer sur that new ones (of the same type) wouldn't vent?