# How do Rechargeable batteries work? (specifically NiMH batteries) **URL:** \ **Category:** Factual Questions\ **Created:** [December 23, 2002, 2:21am UTC](https://boards.straightdope.com/t/how-do-rechargeable-batteries-work-specifically-nimh-batteries/144465 "2002-12-23T02:21:13Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Lobsang](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobsang/32/4067_2.png) [@Lobsang](https://boards.straightdope.com/u/Lobsang)\ **Post date:** [December 23, 2002, 2:21am UTC](https://boards.straightdope.com/t/how-do-rechargeable-batteries-work-specifically-nimh-batteries/144465/1 "2002-12-23T02:21:13Z")
I am watching my new portable TV right now (there’s a film with Sean Connery and Dustin Hoffman in it on) running on the rechargeables from my camera. I started thinking - I will probably be recharging these batteries every single day (maybe several times a day) if I am to use this TV much (It is intended for watching in bed - TV helps me fall asleep). This is a huge increase in frequency from their previous charge rate - rougly one charge every 2 weeks. (Wondering why I shared that. Maybe because I wanted this post to be more than just ‘how do they work’.) Anyway, I then wondered - how [exactly, pedantically] do they work? What is happening to them chemically/physically/electrically while they are being charged? What is happening to them chemically/physically/electrically while they are being used? Will they be able to handle being recharged every day? (the packaging says - good for 1000 charges. but it doesn’t say wheither they can cope with being recharged and used daily) I could probably find all this out by googling (or altavistaing as I prefer it). But I thought a SDMB post would be better all round. As I will get human answers, rather than pre-compiled general purpose answers, and … heck GQ would be nothing if everyone went to google with their questions rather than the SDMB. (There goes maintaining my 1111 post count - level with **Wikkit** ) ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 23, 2002, 2:34am UTC](https://boards.straightdope.com/t/how-do-rechargeable-batteries-work-specifically-nimh-batteries/144465/2 "2002-12-23T02:34:35Z")
Sorry, all I can give you is a [link](http://howstuffworks.lycoszone.com/battery3.htm). It’s a better explanation than I can give, anyway. As for recharging every night, that’s not a particularly demanding use. I’ve never heard fo that being a problem. Batteries can be damaged if drained completely, but a TV will probably shut down before that happens. Over-charging can also cause damage, but if you have a good quality charger it shouldn’t be a problem. You do realize that an AC adapter will be cheaper in the long run, right? ---
**Author:** ![Lobsang](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobsang/32/4067_2.png) [@Lobsang](https://boards.straightdope.com/u/Lobsang)\ **Post date:** [December 23, 2002, 2:47am UTC](https://boards.straightdope.com/t/how-do-rechargeable-batteries-work-specifically-nimh-batteries/144465/3 "2002-12-23T02:47:40Z")
> [@](#): > > You do realize that an AC adapter will be cheaper in the long run, right? I do, (DC actually). I am just so disorganized that It will be a long time or never until I get one. I tried a suitable (same voltage, same size connector) dc adaptor in the TV - nothing happened. So maybe I need to get the exact adaptor quoted in the documentation for the TV - which will make getting an adaptor harder- and therefore more unlikely. My battery charger is as good as they get (quickest time, and stops charging when the batteries are charged) And my mini TV is a brand new £80 casio thing. Is it likely to switch off before the the batteires are drained completely? ---
**Author:** ![Troy\_McClure\_SF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troy_mcclure_sf/32/4150_2.png) [@Troy\_McClure\_SF](https://boards.straightdope.com/u/Troy_McClure_SF)\ **Post date:** [December 23, 2002, 7:54am UTC](https://boards.straightdope.com/t/how-do-rechargeable-batteries-work-specifically-nimh-batteries/144465/4 "2002-12-23T07:54:10Z")
> [@](#): > > \*Originally posted by scr4 \* > **Batteries can be damaged if drained completely** Aren’t you supposed to do that? The way I understand it, the more drained a battery is and the end of each use, the longer is will last in the long run, and each charge will last longer. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 23, 2002, 8:39am UTC](https://boards.straightdope.com/t/how-do-rechargeable-batteries-work-specifically-nimh-batteries/144465/5 "2002-12-23T08:39:29Z")
> [@](#): > > \*Originally posted by Troy McClure SF \* > \*\*Aren’t you supposed to do that? The way I understand it, the more drained a battery is and the end of each use, the longer is will last in the long run, and each charge will last longer. \*\* Well, sort of. It’s safe to completely discharge an individual _cell_. But if the cells are connected in series and you try to discharge this together, some cells will discharge sooner than others. Those will get reverse-charged by the remaining cells, and this reverse charging causes damage. So you can connect resistors to individual AA cells and discharge them independently, but you can’t put 4 cells in a flashlight and let it run down unattended. The benefits of deep discharge is grossly exaggerated anyway. An occasional discharge can help rejuvinate a cell, but if you do it each time it will just shorten the life of the battery. It’s better to just top it off using a “smart” charger that monitors the voltage and shut off when the battery is fully charged. Good chargers also have a temperature sensor and timer to make sure you don’t over-charge. Some companies do tell you to use up the battery before recharging. That’s because those products come with el-cheapo chargers that use a timer for shutoff. Since the charger cannot detect full charge, the only way to prevent over-charging is to start with a discharged battery. My old bicycle lamp (a high-end NiteRider which cost over $100) was like that, and I hated it - a typical example of using the owner’s manual to fix design flaws. (Though I understand this is no longer the case with NiteRider)