3.6v Battery - NiMh or NiCd?

[canadaboy25]

Hey guys, real simple question for you all.  This battery is out of the memory seat controller on my Range Rover.  The battery has leaked and ruined a bunch of traces.  I have repaired the traces but need to replace the battery.  One person online soldered 3 NiMh batteries together.  He reported that it worked until the wires got so hot that the solder melted off?  Someone else replied and said that the circuit is designed for NiCd not NiMh.

When I search the Varta battery on eBay, it shows up as NiMh.  When I search "Range Rover power seat 3.6v battery" it also shows up as NiMh.

Just want a second opinion before I stick a NiMh in and wreck something.

Thanks

[TheSteve]

Assuming it is NiCd there should be no issue at all with replacing it with a NiMh pack.

[canadaboy25]

NiMh does not have Cadmium and is therfore more enviromentally friendly on disposal than NiCd. NiMH has largely supplanted NiCd due to higher energy density and the lack of the memory effect that characterised NiCd. It was common with NiCd to discharge them before recharging to eliminate the battery remembering the state of charge prior to recharging as the point of depletion.

Not being an expert in batteries I can't say there is a reason NiCd must be used in favour of NiMh. It would probably be due to inbuilt charging circuitry if there was a reason. For applications with external charging they are pretty much interchangeable.

With your RR, which you don't say how old it is, It may be so old it was made before NiMh took over from NiCd. The car in all probability used the battery as a memory backup for seat positions and was trickle charged. A NiMh will very likely work fine.

But I do not actually know.

The Range Rover is a 1995.  Yes, the battery just keeps the memory for the different seat positions.  The controller does charge the battery and that's what I'm worried about.  I imagine it is a low current charge so like you said, it should be fine.

Assuming it is NiCd there should be no issue at all with replacing it with a NiMh pack.

Great, that's what I wanted to hear.  I'm guessing the guy that had his wires melt off had another issue than just battery chemistry.

[edpalmer42]

For some stupid reason, Varta reused the same model numbers for NiCd and NiMH batteries in the Mempac line.  Older versions were NiCd, newer ones are NiMH.  I have catalogs from 1988 that are NiCd.  I don't know when the changeover took place.

NiCd memory backup batteries were typically trickle-charged.  NiMH batteries are less tolerant of trickle-charging and require a lower charging rate.  Newer NiMH batteries have improved their tolerance for trickle-charging.

If the guy who had the leads melt off is the one who used Duracell NiMH AAA batteries, they would have handled the NiCd trickle-charge current with no trouble.  Maybe he had another fault that caused overcharging rather than trickle-charging.  You could try something like he did.  Try a NiMH battery, but don't solder it into the board.  Find a spot to put it and buy a battery that fits that spot.  Run wires back to the original location.  Wrap the battery to protect the board from any leaks.

Bottom line here is that NiCd is a dying technology.  You can find them on ebay or aliexpress, but there's no way to tell what the quality will be.  I have a couple of systems that used about 20 NiCd D cells for battery backup.  One I just removed the old batteries and moved on.  For the other, I'm considering a LiFePO4 retrofit, but that requires a complete redesign of the power supply and the addition of new charging and BMS circuitry.

Ed

[glarsson]

For some stupid reason, Varta reused the same model numbers for NiCd and NiMH batteries in the Mempac line.  Older versions were NiCd, newer ones are NiMH.  I have catalogs from 1988 that are NiCd.  I don't know when the changeover took place.

I used these batteries a long time ago. If my memory is correct the NiCd version is blue and the NiMH version is green. Searching for images of Varta Mempac shows blue for older batteries and green for current batteries, so perhaps my memory hasn't lost its content.

[Zucca]

3.6 is equal to Liion battery. Why not squeeze a >100mAh Liion with a protection circuit? 
Can the circuit handle the 4.2V full charge voltage? EDIT: it should, since a fully charged NiXX should go up to 4,5V=1,5x3

Please go soft, I have not too much experience with batteries... 

[Mjolinor]

Nicad all day long. The environment is most suitable for Nicad because, amongst other things, of the expectation that it will go below zero and may get up towards 50c. Nicad handles this sort of thing long term better than NiMh, Liion is just a disaster in the making and will be pretty complex to install.

That is based on experience, not theory though.

[RoGeorge]

This catalog pictures the green NiMH, and in the last column of the table "replaces the old NiCd version".
https://www.usbid.com/datasheets/dsid/60322.pdf

Most probably a NiMH will work, but I just assume.
If you can not find the blue NiCd, it's good to ask the car manufacturer/certified service, or maybe ask Varta if the green NiMH can be used for your car.