Cold charging

Upon getting home from work this evening and putting my Lumicycle
battery on to charge, I was struck by how cold the battery felt.

Are there any particular problems associated with charging cold
batteries? Is it best to charge them while cold, or is it better to let
them warm up to room temperature first, or does it make no real difference.

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Danny Colyer URL:http://www.colyer.plus.com/danny/
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Danny Colyer wrote:
Upon getting home from work this evening and putting my Lumicycle
battery on to charge, I was struck by how cold the battery felt.

Are there any particular problems associated with charging cold
batteries? Is it best to charge them while cold, or is it better to
let them warm up to room temperature first, or does it make no real
difference.

From what I've read on various websites, NiMH and Li-Ion batteres take the
charge better if you first let them warm up somewhat after using them in
wintery conditions. I think 10 degrees C is OK.

~PB

On Fri, 24 Feb 2006, Danny Colyer wrote:

Are there any particular problems associated with charging cold
batteries? Is it best to charge them while cold, or is it better to let
them warm up to room temperature first, or does it make no real difference.

The serious no-no for NiMH and NiCd is charging them when they're hot
(from energetic discharge). I don't think charging them when they're
cold will hurt, but I've never seen anything categorically stating
that.

I let mine warm up a little before charging, just-in-case.

regards, Ian SMith
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Ian Smith wrote:
On Fri, 24 Feb 2006, Danny Colyer wrote:

Are there any particular problems associated with charging cold
batteries? Is it best to charge them while cold, or is it better to let
them warm up to room temperature first, or does it make no real difference.

The serious no-no for NiMH and NiCd is charging them when they're hot
(from energetic discharge). I don't think charging them when they're
cold will hurt, but I've never seen anything categorically stating
that.

A bit OT, but my Nokia mobile was flashing 'battery low' since last
night. Still alive and kicking this morning but still showing '1 bar'
of battery left.
It's been in my pocket all day which is substantially warmer than in
this house and it is now saying the battery is over half full!

I've noticed similar discharging performance with bike lights which die
when out in the cold, but have plenty of juice left when brought inside
to recharge!

pete

Jon is Away! wrote:
Pete Biggs wrote:
From what I've read on various websites, NiMH and Li-Ion batteres
take the charge better if you first let them warm up somewhat after
using them in wintery conditions. I think 10 degrees C is OK.

The very act of charging them with a fast charger will warm them. I'm
not sure of the exact chemistry, but from what I understand I suspect
that allowing them to warm a little first will not hurt, since most
have optimal ranges for charge + discharge.

I wonder two things about the Lumicycle Li-Ion charger:

1. It first tests the battery to decide whether it needs a blast of fast
charging (red mode) before the main, more gentle charge which takes some
hours (amber mode), before trickle charging (green mode). Would it get a
valid reading at the start when the battery is freezing cold?

2. If it starts on amber mode (maybe red as well), the battery doesn't
become warm for some time if it's very cold to begin with, so I think the
charging may be more efficient or "fuller" (?) if the battery was allowed
to warm up naturally before charging.

IIRC they don't discharge as efficiently in the cold, so if they are
getting cool on your ride, you might consider knitting a woolly cover
for them. Jpegs please if you do.

I might take that suggestion quite seriously! My spare DIY NiMH battery
has no insulation at all so maybe I should wrap it in something warm. I
aint doing no knitting though!

~PB

Pete Biggs wrote:
I wonder two things about the Lumicycle Li-Ion charger:

1. It first tests the battery to decide whether it needs a blast of fast
charging (red mode) before the main, more gentle charge which takes some
hours (amber mode), before trickle charging (green mode). Would it get a
valid reading at the start when the battery is freezing cold?

My gut feeling is that it should do, but I wouldn't like to be sure. I
have a feeling that the P.D. will remain the same, but the efficiency
of conversion from chemical energy to electrical energy will be
weakened. I have however drunk a couple of bottles of strong Belgian
beer so this is liable to nothing more than cobblers.

2. If it starts on amber mode (maybe red as well), the battery doesn't
become warm for some time if it's very cold to begin with, so I think the
charging may be more efficient or "fuller" (?) if the battery was allowed
to warm up naturally before charging.

As I mentioned earlier (and others have said the same) charging only
becomes an issue at high temperatures, although it might potentially
take more energy (i.e. longer) when cold. At high temperatures, the
rate of conversion to chemical energy is lower than the energy input
and more heat is produced. In NiMH or NiCad batteries this causes them
to expel hydrogen which reduces the battery's capacity and adds the
exciting risk of a small bang. With Li-ion batteriers this is more of
an issue that can result in a very large bang (see for example: some
Nokia phones). Thankfully your Li-ion batteries will contain circuitry
to prevent this from occuring.

I might take that suggestion quite seriously! My spare DIY NiMH battery
has no insulation at all so maybe I should wrap it in something warm. I
aint doing no knitting though!

Despite the humour it is genuine. Discharge rates are far more
obviously affected by low temperatures, so keeping your batteries warm
on cold nights will allow you to take the long route home. My home made
battery packs (Which closely resemble sticks of dynamite) are made from
plastic plumbing tube, PVC tape and heatshrink which means that the
contents do probably hold temperature for a while.

Jon

Jon is Away! wrote:
IIRC they don't discharge as efficiently in the cold, so if they are
getting cool on your ride, you might consider knitting a woolly cover
for them. Jpegs please if you do.

G
Problem is, I'm so confident about the security of my bike when I'm at
work (covered up, covered by CCTV that I can monitor from my desk,
directly outside the main door and directly beneath my office window)
that I don't bother removing the lights and battery, so by the time I
ride home it's been in out in the cold for 9 hours. I've never had a
problem, though. My commute doesn't take anywhere near long enough to
discharge the battery fully, and it can easily handle 2 days of
commuting between charges.

I might get into the habit of letting it warm up indoors for an hour or
so before charging, though.

--
Danny Colyer URL:http://www.colyer.plus.com/danny/
Subscribe to PlusNet URL:http://www.colyer.plus.com/referral/
"He who dares not offend cannot be honest." - Thomas Paine