How far ahead do you buy batteries?

[Arlin]

We are looking at my options for buying batteries (for wireless mics) in bulk.
I am curious, any recomendations on how many to get at one time?
Any recomendations for how many to keep on hand?

1 month supply?
3 month supply?
6 month supply?
12 month supply?

[Allan Lester]

I am not sure exactly how many we purchase at one time, but I would guess it is probably about a 3 month supply. We go through approximately 20 9V and 10 AA batteries each week just in the main sanctuary so we are definitely buying in bulk!

[DTV-Engineer]

As with film, if you keep batteries cool, the shelf life is greatly increased. If you refrigerate them, there's no technical reason you can't buy a 12 month supply (or more). Just be nice to the folks in charge of the kitchen... and no, don't wrap them in aluminum foil first.

-- Jeff

[kac4him]

Originally Posted by DTV-Engineer

As with film, if you keep batteries cool, the shelf life is greatly increased. If you refrigerate them, there's no technical reason you can't buy a 12 month supply (or more). Just be nice to the folks in charge of the kitchen... and no, don't wrap them in aluminum foil first.

-- Jeff

Has their ever been any study to prove this cause ive always thought this was a old wise tail ,,,,, ever try to start a car on a cold winter day.....

[DTV-Engineer]

Well, it's not exactly an old wive's tale -- but on further investigation, it turns out that you're right: Duracell does not recommend refrigeration, saying that their batteries have a 5-year shelf life. Obviously, things have changed since I sold batteries 25 years ago. (I still stick to that assertion about film, though, with full support from Kodak.)

As far as starting my car, in Syracuse every day from August to May is a cold winter's day! Way back when we did keep batteries in cold storage, we would let them come up to room temperature before using them... can't exactly bring the Saturn into the front hall to warm up, though...

I will now return to my hole in the ground and try for another day when I don't see my shadow...

-- Jeff

Originally Posted by kac4Him

Has their ever been any study to prove this cause ive always thought this was a old wise tail ,,,,, ever try to start a car on a cold winter day.....

Batteries (or most other chemical or electro-chemical reactions) will generally be less 'active' when cold. So, although you might be able to store batteries in the cold, trying to use them in the cold will generally be less satisfactory than in the warmth.

In theory, the chemical reaction in a chemical battery is only 'sitting there ready to go' unless the battery is connected, so it shouldn't really make much difference whether it could be fast or slow, as it's not taking place at all. If you have a battery which discharges when not connected (eg NiCad, NiMH and possibly some older types of battery) then refrigeration may slow this down - but modern alkaline batteries have long shelf lives anyway, so your gain is probably minimal (and refrigeration is inconvenient, and may cause physical stresses and possibly things like crystalisation of electrolytes etc)

Also, here's a list of some typical 'self-discharge rates' (at room temperature):

Lithium Manganese Dioxide (3V) - 1% per year
Alkaline - 2% per year
Zinc-Carbon - 4% per year
Lithium - 5% per month
NiCad - 1% per DAY
NiMH - 2-3% per DAY

So, if you have Alkaline batteries you'll get minimal gain from refrigeration.
If you have charged NiCad or NiMH batteries, a month later you'll need to recharge them. If you refrigerate or freeze them, you can keep them charged longer (but most places I've seen simply recommend recharging them..)

At higher room temperatures you get faster self-discharge rates - eg for an alkaline battery at 'room temperature' you get 2% per year loss. At 85 degrees F they lose 5% per year, but at 100 degrees F they can lose 25% per year. So, if you are in a hot location, without a permanently cool storage facility, it might be best to use a refrigerator. (see http://shop.store.yahoo.com/greenbat...s.html#Freezer)

[pwright2]

Curious as to why you are not using rechargeables? I found the 8.4volt version of NiMH (9v pkg) to be quite reliable. Change every Sunday morning.

I'm new here. Hope I'm not dredging up an old and settled battle.

-----Paul-----

[JerryWThompson]

Paul,

Welcome aboard!!!


YMMV (smile)!!

Some mic's will work fine with the lower voltage and amperage of rechargeables other won't.
_IF_ you have good procedures in place to prevent "memory" problems and being sure they're fully charged __AND__ they will work with your mic's I would (and have) do(ne) it.

Jerry W Thompson

Originally Posted by JerryWThompson

Some mic's will work fine with the lower voltage and amperage of rechargeables other won't.

This is a bit misleading - Alkaline batteries have trouble supplying large currents because they have relatively high internal resistance. NiCad and NiMH batteries can supply much larger currents. (Don't short out a NiCad battery as it will get very hot, very quickly, and can melt quite thick wire (if it doesn't explode first)! They can give hundreds of amps if shorted! - This can be fun if you have some in your pocket along with some coins... (BTDT - ))

This is why 'Ultra' alkaline batteries have been developed for high current devices such as digital cameras - they have a lower internal resistance, so can provide a higher current - but still not as high as NiCad or NiMH

NiCads and NiMH batteries have a voltage of 1.2V instead of 1.5V for Alkaline. However, the Alkaline battery voltage actually averages about 1.2V during its lifetime - dropping from about 1.5V to 1.0V during its discharge cycle. NiMH batteries stay at 1.2V for most of their cycle. Also, if you use it in a high current device, the internal resistance of the Alkaline battery can bring the voltage down considerably.

I've seen figures on the Internet saying that a 2.8Ah Alkaline battery won't power a high power device like a digital camera as long as a 1.8Ah NiMH battery - precisely because of this voltage drop due to the internal resistance. (and I've experienced this phenomenon myself)

Also, NiMH batteries don't suffer from 'memory' problems (NiCads do)

NiCads also contain Cadmium which is a nasty metal. NiMH ones don't - they're probably the 'greenest' general purpose batteries readily available at the moment.

(NiCads have the edge over NiMH batteries on 'high drain' uses like power tools - so your cordless drill will still have NiCad batteries instead of NiMH, as they have such a very high peak current capability)

(See http://www.sonluk.com/faq.htm and http://www.digibattery.co.uk/ni-mh_store1.html )

[[Director] drew ryan]

The issue that we have with rechargables is that when they discharge, they do it rather quickly. we have had instances where they went from full charge to dead without any warning. Not a good thing when the preacher is in the middle of the sermon.

Originally Posted by Drew Ryan

The issue that we have with rechargables is that when they discharge, they do it rather quickly. we have had instances where they went from full charge to dead without any warning. Not a good thing when the preacher is in the middle of the sermon.

Yes, that happens because they have a much flatter voltage curve. Alkalines drop from 1.5V to 1.0V over their lifetime (spending most of the time below 1.2V BTW). NiCad and NiMH stay at 1.2V until very near the end of their 'life' and then drop very quickly.

So, if you have a 'battery charge' meter which expects to see an alkaline battery, the NiMH will stay at 'half charged' until "5 minutes" from the end and then die almost instantly. I believe you can get different types of meters for NiMH which measure things other than voltage. (Alternatively, always use fresh NiMH for each service or day)

[sheldon]

Paul, great list of battery discharge percent! I had a similar chart at our former camera store and wish I still had it.

We use the Maha 9.6v rechargables in our Sennheiser wireless mics with good success. We have 2 of the 10 place chargers and 20 batteries. We swap them between services and only have problems if we forget to change one...

Our set of batteries are getting close to 2 years old and we are considering replacing them. We made our money back in about 6 months (including the chargers) so this is still a good investment for us.