If you’ve been paying attention to the many discussions on this site that related to electric razors you’ll probably notice the terms “NiMH” and “lithium ion” whenever batteries are mentioned.
These terms refer to the two most popular and common battery technologies that are used in these shaving devices. Each technology has its own advantages and disadvantages and it is important that you understand these differences. While I do discuss batteries briefly in my main shaver buyer’s guide, I felt it was worth going into this a little more deeply.
Secrets of NiMH
NiMH is short for “nickel metal hydride” and, before lithium ion became so popular, you would have found these batteries in all sorts of devices that needed practical rechargeable batteries.
NiMH batteries are very energy-dense, which means that weight-for-weight NiMH batteries store lots of useful electricity. They don’t have as much density as lithium however, but that extra capacity on the lithium side comes with some tradeoffs.
Although this generally isn’t relevant to shavers, it’s also important to note that NiMH batteries can be bought in standard sizes such as AA or AAA cells. If you have a travel shaver that uses disposable batteries these would therefore be your best choice.
When you open a shaver that uses lithium batteries, often you’ll find that they have simply soldered together a few standard-size cells. The advantage of this is that you could replace these batteries yourself (in principle). The downside is that NiMH shavers often have bulkier bodies than lithium ones. Lithium batteries are usually custom made and can therefore fit perfectly within the devices. This can also make up for the lack of energy density, by squeezing in more actual battery.
NiMH batteries are also much safer and more stable than lithium batteries. Although both are relatively safe as a whole.
All is not perfect with NiMH batteries, however. There are obviously some cons as well.
If you want a battery that you can leave alone for a long time and then pick up and use, NiMH is not for you. Regular NiMH batteries will lose half their charge by the end of the first month. That’s not great if you want to keep a charged shaver, for example, in your car or at work in case you need an emergency shave.
NiMH batteries have much less voltage per cell when compared to lithium batteries, which means you need more cells in order to match lithium voltage output. This makes NiMH battery packs more complex and prone to failure from bad solder joints, for example.
NiMH batteries can’t handle the temperatures that lithium batteries can, so if things get to hot you may find you shaver slowing down or stopping, even if the charge is not depleted.
The biggest con however, is that these batteries take much, much longer to charge than lithium ones. The capacity advantage of NiMH is almost completely negated by the fact that you can fully charge a lithium cell in a fraction of the time.
Good Guy Lithium
Lithium batteries are the darling of the tech world. Every iPad, iPhone, or other hi-tech device uses lithium ion batteries.
These batteries are reliable and have a very low self-discharge rates. Lithium batteries are smaller as well, in general, and have a higher per-gram energy density than NiMH batteries.
Lithium batteries are also very fast to charge and they are getting faster all the time. Typically a lithium cell will be full after one to three hours of charging whereas a NiMH battery can take a staggering 12 hours to fill up. Yeesh.
Lithium batteries do not suffer from a memory effect either, so they don’t need to be discharged completely before recharging in order to preserve their capacity. In fact, completely discharging a lithium cell can damage it and most devices won’t allow this to happen at all.
Lithium batteries do, however, lose their original capacity the more they are recharged. This usually takes years and modern lithium batteries are rated for hundreds of charge cycles before capacity loss renders them useless.
Bad Guy Lithium
Even though the energy density of lithiums are higher, lithium batteries that you find in devices tend to have lower average capacity for various reasons.
There is also no standardization for lithium batteries, which means you can only get a replacement from the manufacturer of your shaver and only if they still have them. This usually means that when the batteries go in the bin, so does the rest of the product.
Lithium batteries are also a little bit of a safety concern. These batteries are made from a material that is quite volatile and you’ll see articles about smartphone recalls and exploding batteries every now and then on the news. The truth is that the safety circuits that control the batteries are very good and most of the safety issues we see are from low-quality manufacturers in the Far East. So if it’s from a reputable company like Braun there’s usually no reason to have special safety concerns about lithiums. If you are, however, looking at a no-name brand product I would go with NiMH every time, since it’s pretty hard to make those dangerous.
Sophie’s Choice, Kinda
Hopefully you’ll now have a pretty clear idea of what each battery type will mean for you if you choose it. The most relevant facts usually revolve around runtime and charge times. The type of numbers that you’ll find on the outside of the box is not the whole story. While both of these battery technologies will drive your shaver, they are actually quite different and some of those differences are important enough to influence your choices. NiMH batteries are also on the way out, in my opinion, so more and more you’ll find them only in older designs or those that have not been updated in a long time.
Overall, lithium technology is better and that’s why it is so popular, but you should be suspicious of cheap lithium batteries in a way that’s not needed when we look at NiMH technology.