[OT] Charging UPS batteries outside the UPS

[Ben Scott]

On 8/8/07, mike ledoux <mwl+gnhlug at alumni.unh.edu> wrote:
>> I've checked the voltage on the battery, and it's less than 2 volts DC.
>
> In that case, there is almost certainly at least one internal short
> in the battery, and no amount of charging is likely to fix it.  It
> takes some serious work to get a 12V battery down to 2V.

  Even better: That was for each of the 24V packs.  Your comment made
me curious, so I pulled all the wiring off the individual units and
measured each one.  Each unit is giving between 0.5 and 0.7 volts DC.
So either each unit has the same "internal short", or they really are
drained (or something else).

  Te battery was sitting, hooked-up, inside the UPS for I dunno how
long.  You can cold-start this UPS model (turn it on without AC
input), so I expect it is always drawing at least a little power from
the battery (since the UPS front panel is microprocessor controlled).
Maybe that would do it?

> Note well that "sealed lead acid" doesn't necessarily mean "Gel".

  Ahhhh.  Good to know.

> It could be an AGM battery, which will charge just fine with any decent
> PbA battery charger.

  According to a doc on Panasonic website, these are, indeed,
"absorbed glass mat with calcium grids".  Another doc does have dire
warnings about charging, though.  The short version is that without
"constant voltage control" (whatever that means), the electrolyte
breaks down and the battery performance is shot.  Maybe they were
overcharged and that's why their voltage is so low.

http://www.panasonic.com/industrial/battery/oem/chem/seal/index.html

-- Ben