Best rechargeable batteries in winter.

[Neil]

One thing I have noticed with my 2500 mAh Energizer NiMH's is that the battery level indicator on my gps runs quickly down to 2 bars from 4 (within an hour) and then stays there for a very long time - more than 12 hours. (WAAS is off, electronic compass is on, two-way radio is off).
The correct battery type is selected in the gps's "system" sub-menu.
I have cycled these batteries about 100 times and have rarely, if ever, discharged them completely. I have the MAHA C401FS charger.

This would suggest a rapid loss of peak power followed by a very stable output.

One other thing: My new car will only supply current to the charger when the motor is running. With my former car, I could rely on freshly charged batteries evry morning when car camping. Is there a solution?

 

[bill bowden]

Battery indicator

There are several different ways to approach the battery indicator/state of charge problem. The most accurate ones are quite expensive and require both sophisticated equipment and good electrochemical thinking. I believe your unit senses the running voltage fo the battery while the unit is on. This is a pretty good way to do things. In alkaline manganese batteries the voltage commonly drops continuously through the discharge of the battery and thus can match 'state fo charge" quite well. for NiMH cell syou are using the voltage is a little higher at the start and a little lower at the end but quite flat in between and therefore a real challenge to measure by a voltag emethod. The current capability is quite the same. NiCd cells work the same weigh.
Paraphrasing the entire harangue above; "Yes, Neil, you are correct."

WRT the car, If I didn't have daytime running lights I'd leave the ignition on to supply power to the internal electrics to run the charger.

 

[teejay]

Neil,

Even if your car doesn't have daytime running lights (but it does since it's Canadian) I wouldn't leave the ignition on to charge the batteries. Even with everything turned off, radio, lights, blower, etc., there are a lot of other things in a modern car drawing power even if the engine isn't running. Computers (probably three or more in most cars), displays, relays, fuel pump (possibly), etc. You might end up with some nicely charged GPS batteries and a highly discharged car battery overnight.

As far as the accessory plug not supplying current when the car is off, check this out. Some cars have a fuse which can be set in two positions, one which powers the accessories and the dome lights only when the ignition is on and the other when the ignition is off. Check to see if your car has that "feature". When I was selling Dodges, a lot of them came back in a few days because the dome lights didn't work when the doors were opened and the fuse had to be moved to the other position.

teejay

 

[DougPaul]

One thing I have noticed with my 2500 mAh Energizer NiMH's is that the battery level indicator on my gps runs quickly down to 2 bars from 4 (within an hour) and then stays there for a very long time - more than 12 hours. (WAAS is off, electronic compass is on, two-way radio is off).
The correct battery type is selected in the gps's "system" sub-menu.
I have cycled these batteries about 100 times and have rarely, if ever, discharged them completely. I have the MAHA C401FS charger.

This would suggest a rapid loss of peak power followed by a very stable output.

NiMH cells have a rectangular discharge curve. First you burn off a bit of "extra" voltage then the voltage stays constant until the cell is exhausted whereupon the voltage drops quickly. What you are observing it completely normal for NiMH cells. The battery meter simply measures the voltage--a good indicator of remaining capacity for alkaline cells, poor for NiMH, NiCad, and lithium (all of which have rectangular discharge curves).

Here are some graphs of discharge curves of all three cell types: http://www.batteryuniversity.com/partone-22.htm. (I keep suggesting that you guys read http://www.batteryuniversity.com/index.htm--many of my answers to battery questions (plus the parts that I have forgotten ) can be found there. )

One other thing: My new car will only supply current to the charger when the motor is running. With my former car, I could rely on freshly charged batteries evry morning when car camping. Is there a solution?

As some others have noted, the accessory socket (used to be called the cigarette lighter socket...) is switched by the ignition key in some cars. The system voltage is also a bit higher when the engine is running which might also be a factor. So check to make sure that you have juice when the ignition switch is off.

Doug

 

[danno]

a lot of good info in this thread.

thanks everyone, a valuable and much appreciated discussion. I decided to invest in the MAHA - MH-C204W with a bunch of 2500 mAH NiMH Delkin batteries.

Muchos Gracias to all.

 

[DougPaul]

thanks everyone, a valuable and much appreciated discussion. I decided to invest in the MAHA - MH-C204W with a bunch of 2500 mAH NiMH Delkin batteries.

IIRC, that charger charges cells in pairs. This requires that the pairs be evenly matched. Also, what do you do if some applications use odd numbers of cells?

I suggest that you consider a charger with individual charging circuits.

Doug

 

[Neil]

I suggest that you consider a charger with individual charging circuits.
Doug

He's right (unless it's just another lucky guess ). A lot of GPS's use 3 AA batteries, many headlamps use 3 AAA's.

 

[J.P.]

Recently I saw this Solar Charger on sale for $20 and thought it might be greatr for car camping or charging batteries at a base camp -
any body have any thougths on this (I'd appreciate any information)
Thanks
Rick

I had the same thought so I bought this solar battery charger from Campmor. It looks similar to the one you have shown. I found that unless it was in strong sunlight the charging rate was very low. Even thin clouds are enough to significantly reduce the charging rate. You would need to use it above tree line during the middle of the day for it to provide any significant charge so it wouldn't be practical for hiking in the East.