NiMH vs. LiIon

swintonphoto

I use an FL-36 flash with my SLR, and have been using NiMH AA rechargeable batteries to run it. However, according to Olympus my flash will also run on CR-V3 NiMH and CR-V3 LiIon batteries for a much longer period of time than using the rechargeable AA's. I have heard Lithium Ion batteries are better than NiMH. Does anyone know any more about them?

Mr. 2H2O

swintonphoto wrote:

I use an FL-36 flash with my SLR, and have been using NiMH AA rechargeable batteries to run it. However, according to Olympus my flash will also run on CR-V3 NiMH and CR-V3 LiIon batteries for a much longer period of time than using the rechargeable AA's. I have heard Lithium Ion batteries are better than NiMH. Does anyone know any more about them?

Jonathan,
Its a trade-off you'll need to evaluate. Non-rechargeable NiMH and Li batteries will have higher capacities than rechargeable NiMH and LiO. Higher capacities means they'll "do their thing" for a longer, continuous time. It also means you buy new batteries and toss the old ones.

For rechargeable, you can get more capacity from LiO in the same volume than NiMH. Meaning, in a CR-V3 battery volume, you will have more capacity with LiO than with NiMH. You will be able to use your flash for longer continuous periods with LiO. Here's another benefit - if you infrequently use your flash, the LiO will maintain its capacity more steadily than NiMH. In a little more technical version, NiMH has a higher discharge rate than LiO. The resting battery will always discharge itself but the LiO discharges much more slowly.

The downside to that slower discharge rate is a noticeably slower flash recycle time. Your main storage cap wants to grab as much current as it can to recycle itself. NiMH has internal resistance that allows it to flow more power into the cap quicker than LiO. You may see up to 1s delay in flash recycle time for fresh charge.

LiO preforms much better in colder weather, can be charged and discharged for many more cycles (roughly 25% more cycles), does not have a decreasing capacity effect (as NiMH gets older, the capacity dereases with charging cycles but the chemstry can be "reset" with cycling), and LiO has a smoother capacity curve (the voltage decreases more gently with usage whereas NiMH decreases more steeply) - this characteristic affects the flash recycle time as the number of continuous flashes increases. This characteristic may cancel out the slower recycle time experience in newly charged batteries since LiO flash recycle times would be roughly equivalent to a somewhat discharged NiMH pack.

- Mike

Martyn

Mike,

how do you reset NiMH rechargable batteries?

swintonphoto

Thanks for the info Mike. I have been using NiMH rechargables, but i am getting sick of carrying a zillion of them in my pocket and thought switching to the rechargeable CR-V3's would help - and I was debating between the NiMH and the LiIon - I am thinking I am leaning toward Lithium Ion.... Hmmm...

z_28

Martyn wrote:

Mike,

how do you reset NiMH rechargable batteries?

The best way is an use of charger with controlled discharge option.

Bargain way is discharge them manually (in flashlight, radio ...) and
then recharge using lowest current rate, of course if your charger got
multiple charge levels.

Martyn

z_28 wrote:

The best way is an use of charger with controlled discharge option.

Bargain way is discharge them manually (in flashlight, radio ...) and
then recharge using lowest current rate, of course if your charger got
multiple charge levels.

OK. I do this already. I thought there was some magical process i was unaware of.

cmason

Just want to add that you need to be sure that your NiMH batteries need to be rated for your application. So, not all batteries are the same. Play close attention to the mAH ratings. For flash, the higher the number the better, I buy only 2500 or higher, and own only 2700 at the moment. If you just buy batteries at Target, chances are you may have anything from 800 mAH to 2100 mAH. All batteries I have seen carry this rating.

Just googled a search and found this good article:

http://strobist.blogspot.com/2007/09/feed.html

Mr. 2H2O

Martyn wrote:

Mike,

how do you reset NiMH rechargable batteries?

Martyn,
6 deep discharge and recharge cycles - they don't completely reset but it brings the capacities back up over 95% based on the chemists that studied it.

Its pretty hard to do in equipment because often the circuitry will have a minimum voltage cutoff which does not completely drain the batteries. Clamping a short could cause too much internal pressure and thus, a nice little explosion. The best way is to use a resistive load to discharge near the max discharge rate which is based on the manufacturer's specifications (expressed as 2C, 3C, etc).

- Mike