Introduction: Rechargeable Battery Tips

About: Lazy Old Geek

So this Lazy Old Geek uses a lot of rechargeable batteries as probably do many people.

Here’s some that I can think of: laptop, cell phone, cordless phones, cameras, blood pressure cuff, cordless drills, flashlights, cordless toothbrush, cordless PC mouse.

There is a lot of information on the Internet about rechargeable batteries that can be confusing. I am going to try to summarize some of this plus add some tips of my own experiences. I welcome comments with your own experiences.

Some of my information came from these websites:

Battery Info

This website sells batteries and charges.

Batteries in a portable world

Battery University

Both of these websites are sponsored by a company called Cadex that makes battery chargers.

Rechargeable Batteries and Chargers: A Personal Perspective

With many products you have no choice of what type battery you can use, e.g., laptops, cordless toothbrushes. Some like cordless drills you can select the type when you buy, NiCd, NiMH, Li-Ion.

With many products that use standard battery sizes, especially, AAA and AA, you can select the type of battery to use.

Step 1: AA AAA Batteries, Cameras

It is simply incredible how much stuff use these batteries especially if you are a Geek like I am. See pictures. Many products come with alkaline (or zinc carbon) batteries. When they give out, I will always try to replace them with rechargeables. Now I say ‘try’ for a good reason.

The basic alkaline (and zinc-carbon) battery is 1.5Volts.

The basic NiCd and NiMH battery is 1.2Volts so may not work.

 Many newer products, like my Canon camera are actually designed to work with either voltage and battery type but many older products will not or may only work on a freshly charged NiMH and may not last as long. I think I have an atomic clock and a couple of remote controls that won’t work with NiMH and one of my blood pressure cuffs will only work for a short time on AAA NiMH.

Suggestion: If you try rechargeable NiMH and they do not work, then switch back to alkaline.

Or you might try rechargeable alkalines.

Recharging akaline batteries: I do not do this but have read the following.

First, make sure your charger is capable of charging alkalines. Most are not. Second each time you recharge an alkaline, it will have less and less charge and will not last as long.

Third many people report that when they tried to recharge regular alkalines, they leaked. This is rather messy as (I believe) this is an acid. (as a reader pointed out) alkali, a very caustic substance.

Not recommended. Alkaline batteries are pretty cheap anymore.

Digital Cameras:

My Canon camera will work with alkaline batteries or NiMH batteries. This is true of many digital cameras. Most users find that the alkaline batteries don't last as long as NiMH batteries and recommend using NIMH batteries. I do. However, it you suddenly find yourself with discharged batteries, it is nice to know you always have the option of buying and using alkaline batteries.

Step 2: Information by Battery Chemistry


Capacity/mAH: The amount of energy a battery can store. mAH stands for milliAmp Hour or how many milliAmps are available for one hour. A 2500 mAH battery should be able to provide 2500 mA for one hour or 1250 mA for two hours.
C: Is the charge rate of a charger. 1C means that the charge current is equal to the capacity so a 3000mA battery will be charged at 3000mA for one hour. 0.5C means 1500mA for two hours.

Load current or drain: The amount of energy that can be drawn from the battery immediately. A high drain product draws a lot of current continuously.

Self Discharge: Many batteries will slowly discharge if left in storage. This is especially true for NiCd and NiMH batteries.

LSD: A newer type of NiMH called Low Self Discharge. They won’t self discharge as much while sitting on the shelf or being shipped to the customer. While convenient, I don’t think they’re worth the extra cost, yet (2011).

There are two basic types of batteries: primary and secondary.

Primary batteries are disposable. The old dry cells were zinc carbon, the more common are the alkalines.

A newer type is the lithium (not Lithium Ion). The advantage of the lithium is higher drain performance. They are not rechargeable.

Secondary batteries are rechargeable.

There are three main types of secondary (rechargeable) batteries based on chemistry:

NiCd (Nickel Cadmium)

NiMH (Nickel Metal Hydride)

Li-Ion (Lithium Ion)

Do not confuse Li-Ion batteries with Lithium batteries. Lithium batteries are not rechargeable.

Lesser known are:

Lithium Ion Polymer

Reusable Alkaline

NiCd and NiMH batteries


Higher drain performance. They will last longer in higher drain electronics, like digital cameras with flash and cordless power tools.

Can be recharged many times.


Self Discharge Problem: When not being used, Nickel-based batteries will lose some of their capacity over time. Wikipedia says NiMH will lose 5-10% after one day and another 1% every day after at room temperature.

Self Discharge Fix: Some suggest leaving NiMH batteries on a charger, trickle charging. I, and most websites suggest removing the battery within a day of being charged because leaving them on can lead to overcharging and overheating. However, they may require a recharge before usage which is often inconvenient.

Another possible fix is freezing or refrigerating (See separate step).

Memory Problem: NiCd batteries and to a lesser extent, NiMH batteries have something called ‘memory’. What is actually going on is controversial but what it means is that after many partial discharges and recharges, they have less capacity than before. In other words a full charged battery will not last as long.

Memory problem Fixes: To reduce this problem, most websites recommend that NiCd batteries should be fully discharged once a month. Technically, this means the battery is discharged from 1.2 V to 1.0 V. Practically, this means running the device, drill, cell phone, whatever until it no longer works or shuts off. Be careful with some products like flashlights that may discharge too far, much less than 1 V.

Another possible fix is freezing (See separate step).

Now if a NiCd or NiMH battery still has a memory problem, there often is a another way to repair it. This is called reconditioning and will be discussed in another Step.

Li-ion batteries

Good: Higher drain performance.

Li-ion batteries do not have the memory problem.


Lifetime Problem: They do have another problem which is a limited life time strictly due to aging.

Lifetime Fixes: Do not fully discharge the battery.

Leave the battery or device on the charger even after it’s fully charged.

Try to keep battery cool.

Some products can use different types of batteries.

My Canon camera can use alkaline or NiMH batteries.

For some cellphones (I think), you can buy different types of batteries

Products with standard size batteries, AAA, AA, C and D can often work with different types of batteries.

One of the main advantages of using rechargeables is cost. Alkaline and lithium batteries have to be discarded after they are discharged. Rechargeables may be a little more expensive than alkalines but they can be recharged many times.

For most applications I would recommend rechargeable NiMH if they work because:

NiCd batteries contain Cadmium which is toxic. Probably for that reason, they are not as popular and harder to find.

NiMH have less of the ‘memory’ problem then NiCd.

Step 3: Cordless Drills/power Tools

Sometimes you can select a power tool with a specific battery type. A good example is cordless power tools. Drills can be bought using NiCd, NiMH or Li-Ion batteries.

Recommended by and myself:

Buy Li-Ion tools if you can afford it, otherwise buy NiCd. NiCds are supposed to have higher capacity for heavy duty power tools than NiMHs.

I actually own one of each, both made by Makita. The Li-Ion is nice because I can leave it for a long time and it still retains its charge. The NiCd will lose it charge in a few days and have to be recharged.

The manual for my Makita Li-Ion drill says:

Charge the battery before completely discharged.

Change the battery when the drill starts to slow down.

Never charge a fully charged battery. Overcharging.

Let a hot battery cool to room temperature before cooling.

My recommendations Li-Ion power tools:

Do not discharge all the way.

Do not run in hot environment (if possible).

Charge often.

My NiCd drill and batteries are probably 8 or so years old so the batteries don’t last very long. I don't use it very often so I had to recharge a battery before I could use it.

I ran both batteries down a couple of times (see picture) by wrapping some house wiring around the switch and letting it discharge. After the batteries cooled off, I recharged them. They seem to run a little better and don't self discharge as much.

I also tried discharging my cousins Skil drill (see picture) a couple of times and saw a big improvement in run time.

I also stuck one of my NiCds in the freezer. Freezing NiCds is controversial. Several sites, including some manufacturers say you shouldn't do this. Some websites suggest doing this to get rid of memory problems. I tried this but saw no improvements.
Now most websites that do recommend freezing say you should put them in a plastic bag so that they won't absorb moisture. I agree.
Now many websites say freezing will greatly reduce the self discharge problem. This is the main reason I tried this.
PROBLEM: Most websites recommend that you take the battery out of the freezer and let it come back to room temperature. Now, for me this defeats the purpose as I just want to use my drill immediately. If I still have to wait a couple of hours, I might as well just put in on the charger instead of freezing it.
SOLUTION: Well, I decided to try it right out of the freezer. It seemed to work fine. Now I haven't experimented much with this and cannot recommend it.  But, at your own risk, you might try freezing your battery for immediate use. Make sure the battery is dry.

Power tool battery replacements:

Lots of stores and websites sell replacement batteries for power tools. Some places like Batteries Plus will actually replace the batteries in a power tool battery pack.  Most of these battery packs have multiple cells in them. Remember the standard NiCd battery is 1.2V so to get a 12 volt battery pack, there will probably be 10 cells in it.
Now I had a Hitachi cordless drill with two battery packs. They wouldn't hold a charge so I opened them up (see picture). Some of the cells appeared to be dead. I decided to take some battery cells from one pack and put them in the other one to try to make one good battery pack.
Failed: The first problem is that the cells are connected with those metal strips that are mechanically attached to the cell. Well, I was able to solder to them. But the biggest problem is that replacing a couple of  'bad' cells, just caused some others to fail.  After doing some research on battery packs, this is understandable.
Recommendation: If you want to replace cells in a battery pack, replace all of them with new ones with the same capacity and close to the original battery capacity. You might think higher capacity battery cells would last longer but it depends on if the battery charger can fully charge them.

Please recycle all old batteries. My local Home Depot, Ace hardware and Batteries Plus will recycle batteries.

My recommendations NiCd power tools:

Once every month or so, discharge all the way and recharge.

Do not leave on charger once it's charged.

Remove from tool if not being used for a while (Don’t know if this really helps and I don’t do this).

Now if you don't use your power tool that often, you will probably have to recharge it before use.

You might try the freeze method; see caveats above or just stick them in a bag and put them in your refrigerator.

Step 4: Electric Toothbrushes + Phones

So about a year ago, I bought a Braun Oral B Vitality electric toothbrush to replace my old Sonicare that wouldn’t charge anymore. The back says it has NiCd batteries in it. Well, I seemed to have lost the instructions but I remember that it said you can leave it on the charger after each use but that you should run it all the way down, I think once a month. This is consistent with my recommendations for a NiCd battery product.

 Well, I was lucky and I won a drawing for a Sonicare from my dentist. Now the documentation does not state what type of rechargeable battery this uses and I couldn’t find it on their website and didn’t get a response from an email. But I did find one site that said these had Li-Ion batteries in them. The instructions say that you can leave it on the charger anytime it’s not being used which is consistent with my recommendations for Li-Ion batteries.

 My Motorola cell phone has a Li-Ion battery in it. I leave my cell phone on all of the time. I usually charge it when the battery indicator drops one notch. The manual doesn’t say much about it. If your cell phone has a Li-Ion battery in it, I guess I would suggest the same thing:

Charge often.

Don’t let if fully discharge.

Keep it away from hot environments, e.g., don’t leave it in a hot car.

Expect the battery to last about three years at most but don’t buy a spare battery until needed as Li-Ion batteries will lose charge just with time.

I think most cell phones use Li-Ion but some older ones use NiMH. The same suggestions apply except to let it discharge once a month.

My Vtech cordless phones have NiMH batteries. The manual doesn’t say much about charging. Generally what I do is charge a phone, leave it off the charger until it drops a couple of notches, then stick it on the charger.

 It seems like most cordless phones use NiMH batteries.

My recommendations:

Discharge fully, once a month.

Try to keep out of hot environments.

It isn't as important if you buy spare batteries early but it would be better if they were put in a bag and kept in the refrigerator.

Step 5: Laptops

My Lenovo laptop has Li-Ion batteries as, I believe, do most new laptops.

There are some suggestions that most agree:

1. Heat is the biggest problem for loss of capacity. This is probably a good endorsement for laptop coolers. (I don’t use one.) My laptop stand provides convection cooling (hot air rises).

2. Do not fully discharge battery. Partial discharges are fine as they have no ‘memory’ problem.

3. Expect the battery to last about three years but don’t buy a spare battery until needed as Li-Ion batteries will lose capacity just with time.

Theory: When the laptop is connected to AC for a long time, the battery may be fully charged but still on trickle charge. Also when the laptop is in use, the battery’s temperature will be elevated again reducing life.

4. Most suggest removing the battery, if you will use it plugged into AC for long periods of time.

This gets complicating. Most recommend that Li-Ion batteries should be discharged to 40% before being stored. And it is suggested that they be stored in a bag in the refrigerator. A further problem is that they can’t be stored too long. If the battery self discharges too much, it cannot be recharged, so if you store the battery, every month or so, you need to bring it out, let it warm to room temperature and recharge it. Then discharge it to 40% before storing again. This is too complicating for a Lazy Old Geek so I don’t do this.

Others suggest that leaving the battery in all the time is okay. I am of the opinion that most laptop manufacturers are not going to overcharge their batteries once they’re fully charged. I also don’t use my laptop for heavy duty applications like gaming so it doesn't run that hot. My Lenovo laptop has a dual core CPU. Most multicore CPUs run at a lower clock speed compared to single core CPUs. This usually means they run cooler.

Actually, I am just trying to justify not removing my battery because I’m Lazy.

Here is another slightly controversial laptop issue:

Most all laptops have a little application that keeps track of battery charge left. Now, tracking battery charge is difficult to do and this is just a guesstimate at best anyway. However it is generally agreed that as the laptop is used mostly plugged into AC and is not fully discharged, then the accuracy of this application gets much worse. My experience is that this is true. So most web ‘experts’ suggest that every few months, you should do a full discharge so that the application can be re-calibrated.

I guess my recommendation would be if the accuracy of this application is important to you, then by all means, discharge you battery every so often.

Another controversial laptop issue:

Freezing the battery. Some people said that they have restored some capacity by freezing the battery. I haven’t tried this and would suggest it only if your battery is already having problems holding a charge anyway. In other words, as a last resort.

Freezing Tips:

Charge battery if possible.

Let it cool to room temperature.

Put it in a bag to keep condensation to a minimum.

Freeze for a day or two.

Remove and bring up to room temperature.

Make sure it is dry.

Stick it in your laptop and connect charger but do not power on the laptop.

Allow to charge 12-16 hours.

Try it out.

Some people had good luck with this, other not.

Some say they had better luck if this was repeated a couple of times.

Step 6: Freezing NiCd/NiMH Batteries

A 'rumor' is that freezing NiCd batteries will reduce Self Discharge.

Well, I tried this with my Makita NiCd battery pack. It did seem to help. See previous step on cordless drills.

I didn’t know this but there is a lot of Internet controversy that says freezing rechargeable batteries will restore them. I am a little skeptical. Most of the reports are by individuals.

My Method:

Charge batteries first, if possible.

Measure voltage.

Stick in a bag to keep out condensation.

Freeze for a couple of days.

Take out of the freezer.

Remove from bag. Hopefully, there is no condensation, or wrap them in paper towels.

Bring up to room temperature.

Try to charge.

 In the interests of Lazy Old Geek science, I took eight NiMH batteries that wouldn’t charge with my ‘Smart’ charge (see picture). I think I’d charged them on one of my other chargers. They all measured over 1.2V but wouldn’t work in my Canon camera.

I put them in a freezer bag (to keep moisture out) and stuck them in our freezer.

I saw no improvement. They still wouldn't work in my charger or my camera.

I just noticed another ‘tip’. Freeze the NiCd batteries for an hour, then strike them with the plastic of a screw driver to ‘break the crystals’ lose. I haven’t tried this.

Step 7: Battery Chargers

There are thousands of NiMH/NiCd battery chargers out there.

Question: What’s the best one?

Answer: I don’t know.

 One of the problems is that most don’t have much information on how they work and there are no standards on how they describe features. Going back further, there is often no agreement on what methods are best.

A couple of things are generally agreed upon:

Elevated temperature is bad.

Overcharging is bad.

So I can tell you one thing to watch out for.

Chargers that have fixed charge times: Not recommended.

1Hr, 2Hr, 5Hr chargers that don’t say much else. Now these chargers may be perfectly acceptable under ideal conditions which is (probably) a fully discharged battery and for a specific battery capacity.

The problem is how often will you only charge a fully discharged battery. Most people will recharge batteries when they are finished using them or starting a new day. Also the batteries may have a different capacity then what the charger is designed for. This can lead to undercharging or overcharging.

Also charged batteries lose their charge over time. So if you charged up some batteries, then wanted to use them several days later, you would probably want to recharge them. This type of charger will still charge them for the full time which will lead to overcharging and probably overheating.

Features to look for:

Smart charger: This is a little overhyped and could mean anything but is probably better than nothing.

Microprocessor: This is similar to ‘Smart’ but probably means a little more sophisticated circuitry.

Temperature sensor or monitoring: This is a very good feature as it should prevent overheating.

Pulse and/or negative pulse charging: While not necessary, most ‘experts’ think these are good methods.

Negative delta V: This is a very technical concept but a good thing for terminating charging.

Timer protection: This is a good thing if other terminating methods fail.

Individual LEDs or displays: Most AA AAA chargers can charge up to four cells at a time. Some have LEDs for each station which is a good thing because it means that each station is independent of the others. In other words, a good battery and a fair battery will be charged for different times. Now this doesn’t necessarily mean that chargers with a single LED do not charge each station separately. If the charger will only charge two or four batteries at a time and not one, then that means they probably charge the two or four batteries in series. If one battery is in a different state than the other they will not charge evenly.

 Some features that may be desirable:

Discharge/Charge: While not recommended for each charge cycle, an occasional discharge/charge cycle will help to reduce the ‘memory’ problem.

Recondition/RefreshRejuventate: This is usually for batteries that won’t charge or discharge. This will supposedly restore old batteries to new conditions. I don’t have either of these features on any of my charges and cannot say how well they work.

I currently own four standalone battery chargers.

Panasonic 5 Hour:

Not recommended. This is one of those timer chargers that I just complained about.

Panasonic BQ-390A:

The manual (found it online) has no information about charging methods.

But one site says it has smart technology and temperature sensors. It only has one LED but will charge 1,2,3,4 batteries so charges them individually. So this is a pretty decent charger, though probably hard to find.

Ultra super rapid charger: I have very little information on this one. It does have an LED fore each station. It apparently is model ULT31792.

One customer review said it has temperature and uses negative delta V. It will not charge batteries that it considers unacceptable.

Actually, I do like this one and it has been my workhorse.

Rosewill RGD-CT505: I just bought this battery charger as it was on sale at It has individual charge circuits and LEDs and is microprocessor based. It has safety timer, temperature monitoring and ‘fall off’ which I am guessing means negative delta V. It is also supposed to recharge and discharge batteries.

Like the Ultra, it has a feature that if it doesn’t like the condition of the battery put in, it won’t try to charge it and lets you know.

It is also supposed to recharge alkaline batteries but I doubt I will ever use it for that purpose. I haven’t used this enough to get an opinion.

Step 8: Reconditioning

Reconditioning is trying to recover NiCd/NiMH batteries that won’t hold a charge like they used to.

First step: As discussed early, try to fully discharge the battery and recharge several times. Technically, this means discharging a 1.2V cell down to 1.0V. Practically, that means running the device, drill, phone, toothbrush until it doesn’t run anymore.

Second step: If you have a charger that reconditions or restores rechargeable batteries. Try it out. I don’t have one and don’t want to pay $40 plus to buy one.

Possible steps: Some people claim, just freezing batteries will restore them. I had no luck with that method (see picture).

Another: Freeze the NiCd batteries for an hour, then strike them with the plastic handle of a screwdriver to ‘break the crystals’ loose. I haven’t tried this.

Another possibility:

Battery University recommends the following reconditioning method. Discharge the battery at 1C rate to 1V (about an hour). Then discharge the battery at 0.4C rate to 0.4V (about two more hours). Recharge and repeat several times. Now this is a pretty tricky process. This is probably what their Cadex reconditioners use. But I can’t afford $1000-3000 for one of these.

Anyway, I am experimenting with some of this and if I have some success will elaborate in another Instructable.


Well, this came out longer than I expected. I hope some information was useful. Please feel free to send comments.