It seems that NiMh batteries don’t like to be on a trickle charge all the time...
March 14, 2012, by Mike Sessler
Though I’ve been using rechargeable batteries for almost six years now, I’m still learning the best way to maximize their life and run time.
I am a firm believer in continuing education, and we try to monitor the life of our batteries, look at the data and feed that information back into our systems that get tweaked for better performance.
As I said in a previous post about batteries, I was a little disappointed in the life I got of my first set of AAs.
I don’t blame the manufacturer; I suspect we didn’t use them in a way to maximize their life.
So we’ve made a few changes. These changes are based on our usage patterns, so consider them as principles we’re trying, not absolutes to follow.
The first thing I did was to establish a rotation pattern for our batteries. We have 32 AAs in stock, and use 12-16 for a normal weekend.
However, now that I have a team of volunteers who help set up on Saturday (and this includes getting batteries for the mic’s), I noticed that they would gravitate toward some of the chargers and leave the batteries on the other ones.
I suspect this led to some of the batteries being used a lot more often than others. This would explain why I have 12 or so batteries from the original set that still work great, and others that are pretty much done for.
Based on our usage, I designated two chargers (they hold eight batteries each) as Saturday and two as Sunday. That way, everyone always grabs the batteries out of the right chargers, and we don’t end up using the same ones for the whole weekend.
To further randomize the rotation—and because we sometimes have to dip into the other set to accommodate all the mic’s, or because we don’t use them all—when I charge my AAAs for the stand lights, I pull all the AAs out, put them in a box, and randomly put them back in the chargers.
My theory is that this will average out the usage patterns for all the batteries to be roughly equal. While the Saturday on time is a little longer than Sunday, the fact that they get mixed up and put back in different day’s chargers should even that out.
Timing The Charging
My friend Dave Stagl pointed me in this direction; a timed power strip to turn on and off the chargers so they’re not sitting there trickling all week. At the time, it sounded like a good idea. As I’ve done more research, that is confirmed.
It seems that NiMh batteries don’t like to be on a trickle charge all the time, as that can lead to over charging, or just lazy batteries. It is recommended to charge them, take them off the charger, then top them off before use. While I could do that, it’s a lot of work—and you know how much I like to automate things.
This power strip (shown in the photo at right), made by GE and available at Amazon (click here) or your local home center, costs about $30. It can be programmed for seven days, which would be great if you had a mid-week service or rehearsal that you needed the batteries topped off for.
Enter the timed power strip. By setting the power strip to turn on at 5 PM on Friday and off at 5 PM Sunday, I have fully topped off batteries for the weekend, they fully top off on Sunday afternoon, then rest during the week. Of course it’s too soon to tell how this will extend the life, but based on my research, I’m hopeful.
In the past, I recommended leaving the batteries on the charger all the time. I’m changing that stance based on new information and experience. This is not back-peddling or being wishy-washy; I’m simply committed to finding better ways to do everything. As new information becomes available, I update my position. I think that’s healthy.
Also, if you’re interested in learning more about rechargeable batteries, I encourage you to check out Battery University. There is a wealth (and I mean a wealth) of information there about battery technology, chemistry, charging, discharging, etc. It’s pretty impressive, really. And a hat tip to a reader, Frank Dengel for making me aware of this resource.
Mike Sessler is the Technical Director at Coast Hills Community Church in Aliso Viejo, CA. He has been involved in live production for over 20 years and is the author of the blog, Church Tech Arts . He also hosts a weekly podcast called Church Tech Weekly on the TechArtsNetwork.