Best electric energy books according to redditors

I posted the following response in a previous thread on this subject. Also, you can see some actual data that shows NiMH outlasting alkalines in many transmitters.

So, rechargeable batteries for microphones are usually a good idea, but you've got to be aware of some of the quirks of their use.

Cost

My experience with rechargeables is with the Powerex brand. They're commonly seen on Broadway shows and tours. My current show uses 94 AAs and 8 AAAs per show, and I've calculated that it became more cost-effective to use rechargeables at 38 performances -- just under five weeks for us. That includes the cost of the chargers and two sets of rechargeables but doesn't include the costs of shipping new batteries or recycling old ones (alkaline recycling is a whole other topic, though...)

Size

The Powerex brand batteries tend to be slightly larger, physically, than alkalines. I haven't tried other brands of rechargeables to see if they have the same issue. It may or may not be a problem for your particular devices. In our case, they work fine for our Sennheiser 5212s, but they're a tight fit in our Shure UR1s and occasionally they flex the battery compartment in such a way that it loses contact. The problem seems to be getting better over time. They're also a tight fit in our Sennheiser 5200 handhelds, the kind with the removable battery sleds. I know some sound people like to number their rechargeables using a label maker, but I found that the extra bit of diameter made them all but unusable in the Shure UR1s. I have my two sets color-coded, but I just used spray paint to do so (obviously with some tape to protect the contacts). I'd suggest getting a few rechargeables to test fit before you go all out.

Lifespan

The batteries are rated for 500 to 1000 recharge cycles. The lifespan of a battery is improved by using slower charging rates. Under regular use, like on a tour (8 shows a week every week), I'd start to think about replacing them around 12-18 months, or as soon as I notice that the group seems to be running out of battery sooner than normal.

Wrappers

The Powerex tend to shed their paper wrappers after a few months of constant use. They work fine without the wrapper. Unfortunately, while shedding, they sometimes have little bits of paper that can get caught between the battery and the device contacts. This is frustrating, but easily remedied.

Meters

NiMH have a different voltage discharge curve than alkalines and this confuses many battery meters. Some devices have a setting that tells them to expect NiMH, and some don't. I've found that some of my transmitters drop from full to half almost right away and sit on half battery for the whole show.

Duration

Our batteries can go into their transmitters at 5:30 for sound check and last until the show ends at 10:45 without a problem.

Chargers

Get decent chargers that can monitor each battery individually and are able to do a slow/soft charge (this extends the lifespan, at the cost of taking a bit longer to recharge, but it's like 3 hours vs 1.5 hours.) Get enough chargers that you can charge an entire show's worth of batteries at once. We use these chargers. These chargers know when the battery is full and can keep topping it up if necessary.

By the way, I would pay someone actual money if they could make me a NiMH charger that reports charging status either to a network or to an Arduino or something so that I can keep track of my batteries' charging status from my computer.

Self-discharge

This is where I think a lot of people run into trouble. NiMH batteries have notoriously high self-discharge, which is the amount of charge lost simply while sitting. Standard NiMH lose about 20% of their charge after 24 hours off the charger and quickly become almost unusable. This means that you cannot charge up some batteries and then put them in a box or drawer to use as needed. On my shows the rule is this: Batteries go directly from chargers to transmitters.

There is another option, though. You can get "low self-discharge" NiMH batteries. They're sometimes sold as "pre-charged" or "ready-to-use". In the case of Powerex, they're a separate brand, "Imedion". The tradeoff is that they have a lower capacity (in terms of mAh.) We use them here for our wireless comm, where capacity isn't as important as the convenience of being able to load up battery sleds and have them ready to swap. (I also recommend these for use in most consumer electronics, where you're not usually using the device until the batteries are exhausted in the span of a day or two.)

Conditioning

In the old, dark days of using Ni-Cd batteries, we had to fear the "memory effect", where only partially discharging a battery resulted in a diminishing capacity over time. One way to forestall this fate was a conditioning cycle, where the chargers automatically fully discharge the batteries and then recharge them. NiMH batteries do not have this memory effect, and their lifespan is mostly a function of how many times and how deeply they're discharged and how quickly they're recharged. Some people still insist on running NiMH through a conditioning cycle, and even the technical response at Powerex suggests it every ten uses, I'm told. My understanding from my own research is that this is unlikely to make a difference, and actually reduces the battery lifespan because it's another discharge/charge cycle, but I am not an expert and I haven't seen any hard information on the matter. I'm doing an experiment on my current show of only conditioning one set of them every two months (and the other set not at all) and I haven't seen any difference after six months.

TL;DR

Rechargeable batteries are good. Watch out for the self-discharge.

If you're interested in way, way more information about batteries than is reasonable, I recommend Battery University and their book, Batteries in a Portable World – A Handbook on Rechargeable Batteries for Non-Engineers

Edit: I just wanted to mention that Eneloops, which several people have recommended here, are a brand of low self-discharge NiMH.

First of all: good luck. Every week someone new comes into this field with more or less what you just said. However, I do not see a new BMS come out every week. So, logic tells me that very few people who embark in this actually finish. Some do. I wish you the best in being one of those few.

Secondly: "masses of bells and whistles ". Unfortunately, that statement reflect more on your understanding of the problem, than on whether those products do more than is needed. Once you dive into this, you will see that, one by one, each of those bells and whistles is actually essential for the safety and performance of a Li-ion battery pack.

Finally: there are some great books out there that tell you all you need to design a BMS. In your case (small battery) the best book is Battery Power Management for Portable Devices. (I also wrote a book on the subject, but it would be inappropriate for me to link to it here.)

Reading a good book will get you there in 1/10 the time, and increase your chances of success tenfold.

In conclusion, let me tell you: to do the job half right, expect to spend $ 1000 out of pocket, and 1 year of your time (if you know what you're doing) or more.

Maybe, after all, a $ 40 BMS from China that you can get in 1 week is not that expensive, is it?

/ I design Li-ion BMSs for a living.

I don't work with power applications so I'm not sure what specific resources are out there, but the basic technique that gets me by is to research. An IEEE explore account probably goes a long way in opening up access to higher level research, but for the purposes of getting a full set of fundamentals i'd probably just go to the bookstore or libgen and get some power engineering texts, then start going over whichever one is easiest to grok.

Something like this is probably a good resource to have on hand:

https://www.amazon.com/Electric-System-Nonelectrical-Professional-Engineering-ebook/dp/B01N1IUI9O/ref=pd_cp_351_1/135-1299000-4253501?_encoding=UTF8&pd_rd_i=B01N1IUI9O&pd_rd_r=54a75fab-81fb-4939-9b5e-7a9c777be289&pd_rd_w=ofeIP&pd_rd_wg=YZNND&pf_rd_p=0e5324e1-c848-4872-bbd5-5be6baedf80e&pf_rd_r=RTNJERQFZS4V55C6SM9J&psc=1&refRID=RTNJERQFZS4V55C6SM9J