Charging 3.7V lithium-ion battery?

[Terry Pinnell]

Using my Bluetooth-linked GPS unit with my iPAQ 2210 Pocket PC has the
serious downside that the 1000 mAH lithium-ion battery runs out after
3 hours or so, nowhere near long enough for a day's walking/hiking.

I'm considering buying a higher capacity battery (3300 mAH) but that
has the disadvantage that the 2210 would no longer fit its leather
case. So an alternative I'd like to explore is using conventional
(alkaline or NiMH) batteries. The lithium-ion battery is apparently
3.7V. The DC power unit plug that fits the cradle I use when at home
reads 5.28V on my meter. So a 6V set of 4 AA or C or D cells are
candidates, possibly with a diode in series. Has anyone tried this
please? I'm assuming there's protective circuitry to maintain the
appropriate voltage anyway. Presumably the lithium ion battery in
place would get charged simultaneously? Safely?

 

[Arfa Daily]

Terry, the "normal" voltage range of Lithium-Ion cells is 4v2 at full
charge
down to cutoff at typically 3v0. Oddly enough, three times what you'd
sensibly
attribute to a NiMH cell, 1v4 down to 1v0. I'd try three NiMh in a
temporary
configuration to see how it panned out.

As far as charging is concerned, any built-in charging won't match the
proper
regimes for NiMH. There are straightforward non-destructive ways to
determine
what the charger does. Altenratively, put two diodes in series with four
cells
and that way you get a better voltage match without any charging in-situ.

I think that you are mis-understanding what Terry is asking. I think that
what he is saying is that he would like to have a sort of 'battery belt'
arrangement fabricated from dry cells or NiMH or whatever, totalling 6v, to
effectively form a long duration 'field replacement' for the home-based
mains power charger, and plugging into the GPS via the same plug as the home
charger. If that is indeed what he is asking, then there should be no
problem with this. It's basically the pedestrian equivalent of running it in
the car, via a 12v car adapter, which I'm sure is probably available. In
fact, this might be another possibility. Look to see if a car adapter is
available (there's a good place in the UK called
globalpositioningsystems.co.uk) and if so, you could hook it to a small 12v
gel battery, that would be no heavier to carry around than a bunch of dry
cells. That way, your GPS will be powered, and the internal battery will
remain 'topped up'. I do a similar thing when I take my GPS out in the
wife's car, the cradle being normally in my car.

Arfa

 

[Terry Pinnell]

I think that you are mis-understanding what Terry is asking. I think that
what he is saying is that he would like to have a sort of 'battery belt'
arrangement fabricated from dry cells or NiMH or whatever, totalling 6v, to
effectively form a long duration 'field replacement' for the home-based
mains power charger, and plugging into the GPS via the same plug as the home
charger. If that is indeed what he is asking, then there should be no
problem with this. It's basically the pedestrian equivalent of running it in
the car, via a 12v car adapter, which I'm sure is probably available. In
fact, this might be another possibility. Look to see if a car adapter is
available (there's a good place in the UK called
globalpositioningsystems.co.uk) and if so, you could hook it to a small 12v
gel battery, that would be no heavier to carry around than a bunch of dry
cells. That way, your GPS will be powered, and the internal battery will
remain 'topped up'. I do a similar thing when I take my GPS out in the
wife's car, the cradle being normally in my car.

Arfa

Thanks both, very helpful. An hour or so ago I had a recommendation to
try this:
http://tinyurl.com/3p7ugf
at ebay.uk
"This battery extender is ideal for re-charging your iPAQ when you
aren't able to access a mains or vehicle power supply. It takes 4 x AA
batteries and will charge your iPAQ twice with rechargeable batteries
and 3 - 4 times per set of alkaline batteries. It also has built in
overcharge protection, so it stops when your iPAQ is fully charged."

Duly ordered!