How do you make rechargeable batteries last longer?

Gerard – I have also seen rechargeable batteries that refused to charge on a modern charger. You may well be right about the reason. I have disposed of all my old rechargeables recently – they were all over ten years old. They have served me well but new ones seem so much better.

Mixing rechargeable batteries is not a good idea because this increases the likelihood that one will discharge before others and be reverse-charged, as I have described above.

The only benefit of NiCD batteries over NiMH is that they hold their charge longer when not in use. Newer NiMH seem much better in this respect.

Sarah – What Gerard says is quite correct. The capacity of individual batteries in an apparently identical set will differ and this difference becomes greater with age. As the batteries are discharged, one or more can become exhausted while others are still partially charged.

The completely discharged cells are in a Grundig Concert Boy radio, that requires six type D batteries and a Yamaha electronic keyboard that requires six type C batteries. I do not use either very much, but that was why I decided to put in rechargeable batteries. There was formerly a Sony Radio Cassette player used daily that required 6 C rechargeable cells, but when the cassette part died, so did my use.
I think they expire through self discharge more than through usage. These issues have put me off extending my use of rechargeable batteries. Out of over 140 items using 254 batteries I have 6 items using 28 rechargeable standard cells, although built-in and special batteries takes my rechargeable item count to 23.

Self-discharge is a problem with NiCd cells and even more so with NiMH cells, at least the early ones. Rechargeable batteries are at their best if in regular use, which can save spending a fortune on disposables. I used to use rechargeables in infrequently used equipment and I became fed-up because it did not work when needed.

Thanks for this Conversation and feedback, Sarah. The Which? report gives a nice example of a brand where different types of rechargeable cells lose their charge much faster than others. Years ago, I discovered this with Energizer rechargeables. I had one set that was good at retaining charge but the three sets I bought on the strength of this were hopeless.

If I can offer a tip, it’s a good idea to keep sets of rechargeable cells together, either with small coloured stickers or simply marking them with a permanent marker.

Appliances that draw higher currents use up a lot of batteries, but cheaper rechargeables have a much lower capacity than “throwaway ” types. You CAN recharge alkaline batteries e.g. Duracell but you need a dedicated charger, a standard battery charger for Nimh cells won’t work, or even a made-up charger with a higher voltage DC output. I have been recharginf alkalines with success for over 10 years, but you need to charge them before they get too flat. I test C and D cells by connecting a 1.5V/0.25A bulb and measuring the voltage when the battery is delivering current – you can’t use a voltmeter to measure the coindition of a battery that is not delivering current. If the on-load voltage is between 1.00 and 1.2 volts I recharge up to 1.45 volts. If the voltage is less than 1.00V the battery will not take a charge. If you don’;t have a voltmeter you can still do this check. If the bulb is bright the battery is good. If the bulb glows ornage/yellow rather than white, recharge. If the bulb doesn’t light, the battery is past recharging, recycle it.
If you find it’s unsatisfactory putting batteries into a keyboard or other portable appliance, you might consider using a small sla (sealed lead-acid) or other battery type. Many keyboards use a 12 volt mains adapter and 12 volt SLAs are the most common so they are relatively cheap. of course you need a charher, and making up a lead with a fuse and connector may not be your idea of making things easy. They also make rechargeable battery packs with adjustable outputs, so people can recharge mobile phones etc when they are not near a mains socket or a car. This might be an answer to your appliance battery.
Another problem is that people tend to forget how old their batteries are, and they mix old and new batteries, which reduces the overall capacity. It helps to replace them all at regular intervals, maybe every 5 years. Batteries last longer if they are newer and in similar condition, and it’s best to buy batteries of the same make and model.

Tom – Your post reminds me that I used to recharge alkaline cells for my heavily used Sinclair Cambridge calculator back in 1973. Like other calculators at the time, it had a LED display and exhausted a set of four AAA cells within hours. As you say, you have to recharge them before they are flat, but the capacity decreases with every recharge. Eventually I gave up, built a stabilised power supply and used that until I bought a rechargeable calculator a couple of years later. Nowadays I would not bother recharging alkaline cells, preferring to use rechargeables for heavy drain use and non-rechargeables for applications where they will last months.

I keep a 1.5 bulb handy too, but it’s more useful to check the current output on a meter. I use the 10 amp range of a digital meter to check AA and AAA. The peak current and how fast it falls within a few seconds gives a good indication of the condition. It’s not a short circuit because of the resistance of the meter. Unfortunately there is no quick test of the rate at which individual cells self-discharge.

I don’t see the point of a battery operated keyboard if it sits on the desk all day and I know several people who have swapped them for conventional keyboards. On the other hand, a wireless mouse is well worth having.

Hi Wavechange

Thanks for your post, can you explain in a bit more detail your approach to checking current. I diligently check disposables and rechargeables to make sure their voltage is high enough but my son is always complaining that they don’t work for very long in his Xbox controller. I wondered if this was a ‘current’ issue but my physics education has a gap in this area (or maybe it is just the passage of time).

Hi Joel – Using disposables in gadgets that eat batteries, a voltage test is probably enough, providing that you don’t mix types or old with new.

With rechargeables, one cell may start to fail before the others, and checking the current can help to identify weak cells. With AA rechargeables, use a digital multimeter on the 10A DC range and measure the current available from each cell. It’s often necessary to plug the red lead into a different socket to use the 10A range. After charging, measure the current over a few seconds, testing each cell separately. It’s normal for it to fall but look for cells that are obviously weaker than others. Unfortunately, weak cells will only get worse even if the others are in good condition.

Thanks wavechange. The levels danced around for the few seconds rather than fall but there was a big difference between the four, otherwise identical, just charged batteries: 2.3, 3.0, 4.0 and 5.8. I wasn’t sure which to keep using and which to recycle so I have bought a battery tester online.

For those who want to use a multimeter, and have electrical bits kicking about, then this is a good video: https://www.youtube.com/watch?v=HcikzMG7mMU

Having looked at this further, you are right and they are not widely available.

I have a Pure radio. The original NiMH rechargeable battery pack was hopeless but the replacement lithium one (a direct replacement) is far superior. That’s a battery pack rather than individual cells but it has made me interested in lithium rechargeable AA cells. I think I will wait until they appear in the shops rather than taking the risk because a special charger may be needed.

The voltage of a lithium battery depends on the chemistry used. A 1.5 volt cell does not need a built in DC to DC converter. Interesting information about lithium battery technology can be found here, at:
https://en.m.wikipedia.org/wiki/Lithium_battery

Very interesting indeed. Thanks Xopher. I could not understand how a subminiature voltage converter could possibly handle the necessary current.

Hi I’ve several times considered replacing defective cells in “bundled” battery packs, but have stopped short of soldering in replacements because of my concern at heating the battery by using a heavy duty soldering iron and the risk of chemical reaction and explosion. Is my concern founded?

I have never found any problems with safety affecting a cell using a heavy duty soldering iron when connecting replacement cells into a battery pack. The problem, is anything, is maintaining good thermal contact and ensuring all surfaces are clean during the soldering process..

Individual NiMH and NiCd cells can be discharged before soldering and then the only danger is that the local heating could cause damage. It’s obviously best to solder onto the interconnecting strips of metal in the battery to be repaired where this is possible, otherwise use a powerful soldering iron and make connections as soon as possible.

I now use power tools with lithium batteries and they are brilliant compared with the old ones with NiMH and NiCd batteries, certainly for lightweight and infrequent use.

This is a useful reminder that incorrect charging of batteries can cause an explosion, though leakage or irreversible damage are more common problems. It is important not to mix different types of batteries and to use the correct charger. It is normal for batteries to become warm during charging but if they get hot, switch off immediately and let them cool before handling them.

It is generally recommended that rechargeable batteries are not used in smoke alarms.

Sorry Sarah. I’m duplicating what you have already said. 🙁