Lithium-Ion (Li-Ion) vs. Nickel Metal Hydride (NiMH)

[snakyjake]

Getting a new GPS and wondering what rechargeable batteries are best?

 

From my reading on the forum I’ve gathered this info:

• Li-Ion if weight is a priority.

• Li-Ion if temperature is a priority.

• Li-Ion if battery storage is an issue.

• NiMH standard if you want the most mAh, but sacrifice self-discharge.

• NiMH hybrid if you want storage, sacrifice mAh when compared to NiMH high capacity.

 

Capacity

Li-Ion mAh : 1600 mAh

NiMH standard mAh: 2700 mAh

NiMH hybrid mAh : 2300 mAh

 

Voltage

Li-Ion volts : 3.0v

NiMH (1.2vx2): 2.4v

 

Questions

1. What are the runtimes for each battery chemistry? Can I judge by mAh, or do I need to account voltage?

Example: The device may stop working at 2.0v. A Li-Ion has 1v to go, but with less mAh. A NiMh has .4v to go, but more mAh capacity. Which one will last longer until 2.0v is reached?

 

2. Will the device act differently between 2.4v and 3.0v?

 

3. At what point in time do the NiMH low self-discharge become an advantage? A few days, weeks, months? The last report I saw was on flashlights, and I concluded for LED lights the advantages were at approx 6 months.

 

4. What happens to the device when the voltage (capacity) drops? Will the GPS/compass stop working? Or will it become erroneous and lose accuracy? Or just notice the screen fading?

 

Thanks,

 

Jake

[+g-o-cashers]

I'm sure every GPS is different but most GPS's produced in the last few years provide settings for the different battery types. Since, as you point out, each type has a different peak voltage and discharge curve the GPS vendors add settings to the GPS that allow the unit to adapt to the different discharge characteristics of the battery thereby maximizing the the useful life of the battery.

 

Roughly speaking you can calculate the run time of the GPS if you know it's current draw for the settings you care about (compass, backlight, etc). Unfortunately most vendors don't provide this data, they instead provide a battery life in hours which is almost useless unless you know the type of battery, settings of the GPS, temperature, etc. They are usually very optimistic.

 

You shouldn't seen any difference in operation with the higher voltages of Li batteries assuming the GPS supports this as a battery type.

 

Regular NiMH batteries are good for several weeks, maybe longer but you do lose charge over time. Certainly after 6 months they would be dead. If you search around there are places that test the discharge of NiMH batteries over time.

 

Most GPSs will turn off when the voltage drops below a certain level. Some try to turn off features like backlight or audio tones before they go dark.

 

GO$Rs

[+Team CowboyPapa]

sj, whole bunch on batteries regarding the DeLorme PN-20 here:

http://forums.delorme.com/viewtopic.php?t=8919

 

It should also be generally applicable to the -40.

[Ken in Regina]

A couple of comments... First, on the voltage issue, there is a FAQ on Garmin's site that describes a problem with startup. Some new Lithium Ion batteries can provide as much as 1.6V. A pair of these batteries will cause the GPS to shut down immediately upon detecting the high voltage at startup. Garmin recommends running the batteries down a bit before using them. They say it won't hurt the GPS because it shuts down as soon as it detects the over-voltage condition, which is basically immediately.

 

Second, Eveready advertises that their Energizer Lithium batteries will last up to 8 times as long as their top-rated alkaline cells. I bought a pair this fall and that was not my experience. I was replacing a pair of cheap Superstore no-name alkalines (40-pack for $13 Canadian) with the Energizer lithiums ($10 Canadian). The Energizer Lithium batteries gave me approximately double the use. I was not impressed.

 

I have no idea how representative that experience was but I'm sure not going to use Lithiums again. I use rechargeables (NiMH) when I'm near my charger. When I'm on the road I just grab a 40-pack of Superstor no-names or a 48-pack of Costco's house brand (Kirkland) and I'm good for my GPS, my digital camera and my cell phone (using an external battery pack with 4 AA cells in it to recharge).

 

For anyone who uses NiMH rechargeable batteries it's important to have a good charger. The cheap chargers that are often bundled with a set of batteries almost never fully charge the batteries and they do not have any way to exercise and analyze the batteries to either restore them or tell you when to get rid of them.

 

...ken...