Tech: Does mAh make a difference in batteries?

Subject: Tech: Does mAh make a difference in batteries?
From: GUEST,Jack the Sailor
Date: 03 Oct 08 - 02:14 PM

I have a camera that had a 3.7v 740mAh battery come with it. Can I substitute a 3.7V 1000mAh battery?

Are the mAh's Milli Ampere Hours? doesn't just mean the higher mAh battery will last longer?

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Micca
Date: 03 Oct 08 - 02:25 PM

It means exactly that Jack and as long as the Voltage matches the more mAh the better

Subject: RE: Tech: Does mAh make a difference in batteries?
From: GUEST,Auldtimer
Date: 03 Oct 08 - 03:18 PM

"the more mAh the better" ?
Only as long as your battery charger is up to the job. 740 up to 1000 should not be too bad though.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Bernard
Date: 03 Oct 08 - 03:46 PM

Yes, increasing the capacity will mean they last longer - but they'll also take longer to charge. That might sound obvious, but some chargers work on a timer rather than by sensing the current flow, and so would not fully charge a higher capacity cell/battery.

If you're using individual cells (AA for example), just be careful not to mix different capacity cells in a set, or you'll end up with a lower rated cell 'reverse charging' and getting very hot!

This is because it fully discharges before the rest of the cells, and literally starts to charge backwards - the '+' terminal will be '-' and vice-versa. Sounds daft, I know, but it's true!

It's a worthwhile investment to buy a simple battery checker, so that you can easily check the charge-state of your cells.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: GUEST,iancarterb
Date: 03 Oct 08 - 07:12 PM

All the needed facts and cautions above. Great mudtechers!

Subject: RE: Tech: Does mAh make a difference in batteries?
From: EBarnacle
Date: 03 Oct 08 - 08:12 PM

The same applies to cell phone batteries.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: The Fooles Troupe
Date: 03 Oct 08 - 08:35 PM

As far as AA cells go, about the highest accurate stated energy rating for rechargeables is 2500 mAh rating (Quality cells - anything go for cheapies).

"Battery chargers" for modern advanced rechargeable cells are no longer 'cheap and nasty', they can be internally quite complex, even using PICs (programmable ICs - like tiny computers) to give multiple rates/levels of charging current, depending on the initial battery state at start of charge, and even a 'holding' charge - the good ones also cannot overcharge and damage the cells either.

A good investment if you want to use the cells a lot for best economy.

Note that most rechargeables will lose a % of charge all the time till totally discharged - the LiMH ones lose a much lower percentage. You cannot store charged rechargeables for months and then expect them to be holding a full charge.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: GUEST,Jack the Sailor
Date: 03 Oct 08 - 08:57 PM

I have a battery checker I've just charged the battery with the charger that came with my camera. My Digital multimeter gives pretty much identical readings for the newer $7.00 battery and the $40.00 (to replace) battery that came with the camera. The camera works like a charm with both. So far I am pleased.

Its not an AA. Its a li-40/42B or NP45 lithium ion camera battery. The camera manual recommends draining before storage and a full recharge before the next use.

Subject: RE: Tech: Does mAh make a difference in batteries?
From:
Date: 05 Oct 08 - 08:21 PM

Jack, that last recommendation is a good one. But they mean long term. If you're going to put the camera away for a week to a month don't worry about it, but if you're wanting to store it until next year's vacation, do as they recommend.

Also, the digital multimeter only gives the open circuit voltage, ie battery without a drain/load on it. Best test is to put a load on it, a resistance of some sort, of appropriate wattage, to see how long it holds that voltage with the load in 15 min and half an hour. That will determine how good the battery holds a charge in working conditions.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: GUEST,Jack the Sailor
Date: 06 Oct 08 - 12:40 AM

Today, I plan to test the battery by putting it to work. Today. Lets see if i can take a couple of hundred snaps with it. :-)

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Leadfingers
Date: 06 Oct 08 - 01:52 AM

Bear in mind that a COMPLETE discharge is advantageous before recharging . If the charger has a Discharge Option , use it , other wise a Resistor Load across the battery for a couple of hours or so should do the job . I have a few of the two and four battery holders
to do the job for me .

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Murray MacLeod
Date: 06 Oct 08 - 02:35 AM

I have recently bought three Makita cordless drills and the manual recommends charging them as soon as they start to show signs of winding downm and specifically advises against full discharge.

A drill is not a camera, of course, and these drills use Ni-Cad batteries , not Li-Ion.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Richard Bridge
Date: 06 Oct 08 - 02:42 AM

The clever gadgets that will re-charge non-rechargable batteries recommend charging before complete discharge, too.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: The Fooles Troupe
Date: 06 Oct 08 - 02:45 AM

... ok... then what happens when you have a half full one, then....

um...

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Bernard
Date: 06 Oct 08 - 06:52 AM

Probably the same as when you have a half empty one...!

;o)

Subject: RE: Tech: Does mAh make a difference in batteries?
From: JohnInKansas
Date: 06 Oct 08 - 07:55 AM

It is of some importance that you know which kind of batteries you have. In general, you need to be sure that you are using a charger that is designed for charging the kind of battery you are using.

NiCad (Nickel Cadmium) batteries are still used with some devices. They have a fairly good "energy density" and are generally suitable for devices with moderately high discharge rates (high current) such as "cordless drills" and other tools. They are subject to fairly rapid "wearout" and accept only a limited number of recharge cycles.

Most devices currently using NiCads use "batteries" containing multiple cells to get a higher voltage, and frequently are in "special" package configurations to fit a particular tool - and requiring a special charger that comes with the tool (or can be purchased separately). If you have single cell NiCad batteries, they probably benefit from discharge before recharging, but if your "battery" consists of multiple cells the mfr may recommend NOT DISCHARGING fully, since discharging a series stack of batteries to zero may "reverse charge" one or more "weak" cells in the stack.

NiMH (Nickel Metal Hydride) batteries are probably the most common single-cell rechargeables now, and are what you'll find in AAA, AA, C, and D cell forms. The single cell forms of NiMH are where you're most likely to find variations in mAh capacities. I have AA NiMH cells with "capacities" ranging from 1800 mAh to 3400 mAh. Recent shopping expeditions have found a range from about 2300 to 3400 mAh(for AA size) currently for sale in my area.

A particular problem with NiMH cells is that they self-discharge fairly rapidly during storage. If the device you use them in has low to moderate power requirements, the "reserve" cells you charged at the same time that you put "fresh ones" in the device will probably be just as dead as the ones in the device when it's time to swap batteries. The usual recommendation for NiMH cells is that you store them (for long term storage) discharged, and only charge them immediately before use. They "wear out" after a number of recharge cycles, but have almost unlimited storage life if kept discharged. On the other hand, a "new" NiMH battery will generally show slightly better performance after a few discharge/recharge cycles, so using the same batteries, or a pair used in alternation, until they wear out is usually a better idea than trying to keep several sets ready to exchange in the device(s).

Especially for NiMH batteries, my experience is that there is a significant difference in the chargers found at market. Some do work a lot better than others, so if you experience poor battery service it's as likely to be the fault of the charger as poor battery quality/condition. A charger that takes 8 hours to charge AA batteries generally will give better battery performance than the one that promises a "quick charge." I've found a couple of chargers though that take very long times to charge and still don't seem to do it right.

Lithium Ion (Lithium) batteries usually come in multi-cell packages, and are most used in low-current devices like cameras and computers. They accept relatively high charging rates, and have pretty good "energy density," but older forms are not too tolerant of high discharge rates.

Some portable tools have begun to appear with Li batteries that do give better tool performance than the NiCad packs they replace, but at significantly higher cost. As with the NiCad packs, the battery packages most commonly found require that you use the charger that comes with the battery.

Many devices that use Li batteries have "built-in" chargers. (You may have to connect a wall wart to your phone - or computer - to charge the battery, but it only supplies the voltage/power for the built-in charger inside the phone/computer. The bult-in charger manages the actual battery charging.) A few devices may come with an external charger for Li batteries, but it's usually due to a proprietary battery package configuration with specialized shape and/or connection details.

For devices that really require high current (actual high power) there still is no cost-effective replacement for modern lead-acid batteries, although I doubt that many here are worried about recharging fork-lifts, golf carts, or electric scooters. There are undocumented claims that high capacity Lithium Ion batteries are "coming soon," and we all hope to live long enough to see them. For current "current" users, lead is far from dead.

John

Subject: RE: Tech: Does mAh make a difference in batteries?
From: EBarnacle
Date: 06 Oct 08 - 09:59 AM

I have found that when a rechargeable battery is not accepting a good charge that it can be remade to almost full capacity by freezing it for several days. I don't know why. I just know that I have saved batteries for marine radios, computers, cordless drills digital cameras and cell phones this way. Discharge the battery before putting it in the freezer. If the battery is not removable, put the whole thing in the freezer. Plastic bags are a good idea to isolate the battery from its surroundings.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: JohnInKansas
Date: 06 Oct 08 - 10:26 AM

EBarnacle -

Some sources also suggest the deep freeze as a last resort for getting the last possible spinup out of failed/failing hard drives. As with batteries, nobody offers a good theory for why it sometimes works, and "unbiased" pundits may accuse you of bizarre superstitions when you claim it did. ... but ...

John

Subject: RE: Tech: Does mAh make a difference in batteries?
From: Newport Boy
Date: 06 Oct 08 - 11:29 AM

John's summary covers most of the ground. For a little more detail, including figures on % discharge over time and recommendations for storage, look at this Glossary at Eurobatteries.com

Phil

Subject: RE: Tech: Does mAh make a difference in batteries?
From: The Fooles Troupe
Date: 06 Oct 08 - 11:41 AM

"it can be remade to almost full capacity by freezing it for several days"

One theory is that the spicules which short the charge are disrupted by the freezing process.

Subject: RE: Tech: Does mAh make a difference in batteries?
From: MaineDog
Date: 06 Oct 08 - 08:46 PM

There exist "slow discharge" Ni mh batteries, which don't lose their charge as quickly when just sitting around. Even though they are not rated as high as the newest high capacity jobs, they will last for months in your camera or recorder and still have lots left when you need it.
MD