DIYbanter - View Single Post - APC UPS -- replace battery, or...?

Benderthe.evilrobot

"mike" wrote in message
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On 1/16/2017 9:01 AM, wrote:
On Monday, January 16, 2017 at 10:22:11 AM UTC-5, Phil Hobbs wrote:

It would have to be a pretty small car battery for a 750 VA UPS to do
any harm to the car.

I am thinking more of some level of dead-short or similar.

Peter Wieck
Melrose Park, PA

Have you tried the power interrupt with a very light load, like
a 4W night light? That might give you a clue whether the system
will run with a new battery.

Use a voltmeter to measure the voltage on the UPS battery when
unloaded. Turn on the system, do the power interruption and see what
the battery voltage does. Try it with a very light load.

If you're paranoid, put a 20 amp fuse between the car battery and
ups battery.

Another option is to hook a car headlight or some other heavy load
directly to the UPS battery to see if it is good.

I've seen some pretty clapped out batteries light a H4 headlamp bulb with no
problem - its not a reliable test.

A UPS battery should turn over a typical motorcycle starter without any sign
of being sluggish.

Some UPS units play dead if there's high internal cell resistance.

Another point many overlook - Ah capacity falls as current draw rises.