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So I have 2 sonic toothbrushes, one powered by NiMH the other by Li-ion batteries (waterpik & philips). The base stations (with charger in them) look so convenient and just lure me to store devices on them.

I've studied the manuals and could not find whether device is designed to be kept on base station indefinitely or device should be stored off the charger until 'battery-low' signal.

So the question is: does it degrade the battery considerably if the device is stored all the time on the charger station?

Charge time for them is around 12-24 hrs. They use inductive charging method (I mean there's no port/plug you physically connect charger to, you just place device at or near charge station).

UPDATE So I've contacted customer supports of both companies, and asked is brush designed to be stored on charger and how long the battery is to serve.

...and basically they both said brush is designed to be stored on the charger. Phillips says there's 2 year warranty for the battery, Waterpik support mentioned it should last 3-5 years.

While this is a great battery life (longer then on my ihpone 5s lol) as @BillDubuque and @FakeMoustache mentioned they might serve even longer if stored off charger.

Would still be interesting to know what difference two charging strategies make on the battery life.

UPD could anyone please un-close this question? I'd love to accept answer from @BillDubuque as the man provided lots of useful info in comments, I'd like him to get his reps.

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  • \$\begingroup\$ See This \$\endgroup\$
    – Adam Z
    Commented May 16, 2016 at 9:56
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    \$\begingroup\$ @DaveTweed I don't agree that this is a question about the use of an electronic device. Rather, it is a question about optimal charging strategies for batteries, so it should be considered on-topic. In any case, I think the community should have decided topicality, not a single user. \$\endgroup\$
    – Bill Dubuque
    Commented May 16, 2016 at 16:25
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    \$\begingroup\$ @BillDubuque: Whether or not the toothbrush is stored on its charging base has very little to do with the charging strategy used for the battery, except in the very limited sense that if it is not on its base, it can't charge. As I explained in my answer, the actual battery charging strategy is determined by a controller inside the toothbrush. This question is NOT about the design of that controller. If it were, it would be on-topic. \$\endgroup\$
    – Dave Tweed
    Commented May 16, 2016 at 16:57
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    \$\begingroup\$ @Dave But your answer is incorrect and misleading. Unfortunately I cannot correct it since you closed the question a minute after you answered it. In some SE communities such behavior is greatly frowned upon ethically. Not to mention that is not exactly a great way to attract further expertise to the site on topics where community knowledge is patchy. \$\endgroup\$
    – Bill Dubuque
    Commented May 16, 2016 at 17:33
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    \$\begingroup\$ @DannieP Re: your update. Of course, generally, CSRs are not experts on battery technology. Besides the strategy I mentioned in my my other comment, you can also prolong Li-ion battery life by keeping the average capacity around 50%, and minimizing the depth of discharges. But this is not something that is easy to achieve in a device like a toothbrush. Done optimally, you might get 5x battery life or more, but at a cost of inconvenience. \$\endgroup\$
    – Bill Dubuque
    Commented May 27, 2016 at 21:46

2 Answers 2

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For the NiMh one I would not leave it charging all the time. Although NiMh cells do not have much "memory effect" in my experience they last longer if you do not charge them after every use. I would use them until you start noticing they're running empty or you think they will be empty soon. You don't have to run then completely down to where the device stops working though (that was only needed with the old NiCd cells).

For the Li-Ion one you can recharge it after every use if you like, these cells do not mind being recharged all the time. The charging circuit will stop charging the cell when it's full anyway.

But if you would apply the strategy of the NiMh (dicharge until almost empty) to the Li-Ion it would also last a long time. I have a (Philips) shaver with a Li-Ion cell and I only charge it when it is almost empty (the shaver has a display so I can see when it's almost empty). It is lasting for more than 5 years already ! OK, I notice that the cell is wearing out a bit but I can still shave for weeks after a charge.

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  • \$\begingroup\$ Thanks for the quick answer! Could you add any more from your experience with NiMH, how big of difference that make depending on how you charge them? \$\endgroup\$
    – Dannie P
    Commented May 16, 2016 at 10:16
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    \$\begingroup\$ No, I cannot, since I have no experience with using NiMh cells that way since I know they do not like recharging all the time so much. I also have noticed that there is a large quality difference in NiMh cells, some last forever, others last much shorter. The Philips ones seem to be very good quality btw ! Some have high self-discharge (empty after 2 months) others keep their charge much longer. So no I cannot say anything usefull in this regard, just tips on what I think is the best way to treat them. \$\endgroup\$
    – Bimpelrekkie
    Commented May 16, 2016 at 10:26
  • \$\begingroup\$ @DannieP If you want to prolong the life of your Li-ion powered devices then you should not always recharge after use. The rule of thumb is that to maximize life you should minimize the time the cells spend at high voltages and high temperatures (since it accelerates internal parasitic reactions). If you always recharge after use then you are instead maximizing the time it spends at high voltage - which is the worst way to store Li-ion cells. \$\endgroup\$
    – Bill Dubuque
    Commented May 16, 2016 at 16:08
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Yes, electric toothbrushes are designed to be left on their chargers at all times when not in use. They have internal charge controllers that protect the batteries, and often have a status light of some sort that indicates whether they're actually charging.

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  • \$\begingroup\$ Dave, thanks for the answer. Two follow-up questions: 1) I see you put the thread on hold as off-topic, please suggest a better forum then electronics for the next time. 2) Any link/reference to back up the point? Cheers \$\endgroup\$
    – Dannie P
    Commented May 16, 2016 at 12:15
  • \$\begingroup\$ 1) It would be better to ask the manufacturer directly. 2) You said you studied the manual, but the information should really be in there. \$\endgroup\$
    – Dave Tweed
    Commented May 16, 2016 at 12:24
  • \$\begingroup\$ 1) I've asked for a community; sometimes you want ask a community, not the manufacturer. Good idea though. 2) Yes, I did. If you have any references to back up the point please share, having this question answered here might benefit somebody else. \$\endgroup\$
    – Dannie P
    Commented May 16, 2016 at 12:39
  • \$\begingroup\$ @DannieP This does not correctly answer your question "does it degrade considerably..." See my comment on the other answer. \$\endgroup\$
    – Bill Dubuque
    Commented May 16, 2016 at 16:12
  • \$\begingroup\$ So its not going to burn the house down as I left it on holiday? \$\endgroup\$
    – SuperUberDuper
    Commented Dec 4, 2017 at 13:49

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