>...  a design ... has 6 "D" size NiMH batteries in series and in his desig=
n there are
> three sets of two cells contacted with 6 spring clips. These will be in
> a sealed compartment with no user access. The batteries will never be
> overcharged or over heated but I warned him that they would have a high
> failure rate due to exudate from the batteries interfering with the
> contacts. > Am I being overly cautious?
> All battery tools I see have welded tabs - never spring contacts.
> I will admit that all the ample corrosion products I have seen were with
> NiCD batteries

NimH also produce 'exudate'.

Murphy loves non solidly joined contacts.  Especially ones that can't
be got at to fix.

But/and, I'd severely question the wisdom of using 6 x NimH in series
instead of eg LiIon unless there is a good reason to do so.

6 x 1 =3D 6 min
6 x 1.25 =3D 7.5 max loaded
Maybe 6 x 1.3 =3D 7.8
..
2 x LiIon =3D 6 min, 7.2 hauling, 8.4 max.

In terms of powering equipment most loads will not differentiate
between the NimH and LiIon voltage range.

6 x 1 =3D 6V at min cell voltage
5 x 1.2 =3D 6V with one cell dead.
ie it is easy for the pack to work one cell all the way to zero and
still APPEAR to be a valid pack.
If battery balancing is not used as part of the charging scheme
imbalance will occur over time and 'the runt' will be pushed to below
spec. It will die early and the battery will die early.


 Russell McMahon
--=20
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