Understanding Discharge Curves
Another main factor in the “I’ve been burned” phenomena is the different discharge curves between an alkaline and NiMh battery. An alkaline battery drops off in a pretty linear fashion.
A NiMh, on the other hand, quickly drops from full voltage to something less than that and holds there for a long time. When it drops off, it drops of the cliff very quickly.
Most battery meters in wireless mics are calibrated to the discharge curve of an alkaline battery. As the voltage drops off, the meter can predict approximately how long the battery is likely to last.
However, with a NiMh, the voltage holds, then falls off very quickly. This is why it’s not uncommon to see a NiMh battery go from 4 bars to 0 in 5 minutes. The meter has no idea how to know where the battery is.
Some newer mics have battery meters that can be switched between alkaline and NiMh (the Shure UHF-R does for sure), and those can be a help.
However, there’s still no substitute for doing some testing and finding out how long they last in your mics.
Once determined, you know how often you need to change them, regardless of meter reading.
For example, I know that the Powerex and Sanyo 2700 mAh batteries will run a good 12-14 hours in our mics. So, I can feel confident putting them in Saturday afternoon for rehearsal and letting them run through end of service (about 4.5 hours total).
I can then put in a fresh set Sunday morning and be fine through the end (about 5 hours total). I don’t expect to ever have one go down, unless it’s a fluke. But again, that happens with ProCells, too.
Those are some basic principles for the proper care and feeding of NiMh batteries.
If you haven’t tried them lately, you should really give them a chance.
Are you a fan of rechargeable batteries? Have you recently switched? Let me know in the comments below!
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.