I have a hand held Garmin GPS with built in compass. Each time the 2 AA cells are changed the compass needs to be recalibrated. Instead I would like to demagnetise my collection of rechargeable NiMh AA cells - Will this affect the working of the calls ? I assume the iron is in the casing rather than the chemicals but just wanted to make sure.
Thanks Dennis

 

From Garmin:
"So every time you change your batteries or you move more than 100 miles since you last switched on your GPS please do calibrate your compass".
My guess is this has nothing to do with any magnetic field effect from the batteries but rather the device internal memory which is always active even when the device is off. Removing the batteries allows the unit to lose memory (compass headings) much like if the device is off and you power it up at a distance greater than 100 miles from the last power up. Have you read the owners manual for your specific model?

Maybe another member has a thought but I don't see the batteries as a problem and I have never heard of demagnetizing batteries.

Ron

 

Thanks for your reply Ron. The manual (Garmin eTrex 30) says to recalibrate "after moving long distances, experiencing temperature changes or changing the batteries" As a test I set up a Silva baseplate compass (Type 4/54) on a wooden bench and approached it from the east with various AA cells. All the cells caused at least a 10 degree deflection and several caused a 90 degree shift. The energizers (10 tested) were generally best , of the 4 the Duracells tested one made a 90 degree shift and the rest varied. Uniross Hybrio (4 tested ) had two with large deflections and a pair of Sanyo Eneloops had about 30 degrees. Strangely around 2/3 of the cells had the North pole at the positive end. reversing the cells deflected the needle a similar amount in the opposite direction.

I also tested 4 primary cells Duracell Procell which had similar widely varying results. I also found a used Rayovac that caused a large deflection and passed it over my home made demagnetiser several times and this reduced the deflection to just a few degrees.

Is their any internal battery component that would be likely damaged by demagnetising ? My guess is probably not but maybe the Nickel component might be disturbed. it could be that its just the case that is magnetic - certainly an old failed cell could be picked up by a magnet.

Thanks Dennis

 

As a test I set up a Silva baseplate compass (Type 4/54) on a wooden bench and approached it from the east with various AA cells. All the cells caused at least a 10 degree deflection and several caused a 90 degree shift.

That is interesting and something I never gave much thought to so thanks for sharing it. While I never gave any thought to demag of a battery I really can't see where it would hurt the batteries. Don't take that as gospel though. Somewhere around here I have an old GI compass which is a pretty good one. Next time I see it I'll have to try a few experiments.

As to actual demag you could make or find a coil of wire, run an AC current through it and slowly pass the batteries through the coil center. That may work as a quick and simple solution.

Ron