It is very tricky to put lead-acid batteries in parallel without having
a charger for each string.
By the time you are done getting chargers for your batteries and
converters from the serial string voltage (48V likely cheapest) you
will have spent more money than the battery capacity is worth, given
that we are talking about aged batteries.
I would leave th UPS alone, possibly using it for something else in
the house, and get a battery-backed power-supply of the kind used for
fire-alarms.
That is basically a load-tolerant charger and a 12V lead-acid battery
in a box.
You can also buy or build a charger yourself if you want, a float
charger is just a 13.8V supply, but you should temperature correct
for battery temperature for maximum lifetime.
If you use a 13.8V charger without boost mode (14.5V) you don't need
more than a couple of diodes in series to get the 12V for your disks
(remember a fuse though).
The 5V for the disk can probably be supplied by the regulator on
the NET5501.
So total parts-list:
13.8V powersupply
12V Lead Acid battery
two 5A silicon diodes
3A slow blow fuse
See also: http://phk.freebsd.dk/soekris/ups/
Poul-Henning
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
[email protected] | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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