old car batteries?

[(unknown)]

I am using old car batteries for my powersystem, because i get them for free at the garage and i think they are still good, even better then a frend has in his car. But i was wondering if they consume more energy with loading the batteries then new batteries, because then i will buy 1 new one in stead of 3 old ones. And i was wondering if when i am using 3 or more batteries, who are not the same, in my system i can load them simultaneous?

[tecker]

  Put a full charge on the old batteries and test with a Hydrometer . Or you can test the impedance by using a standard trickle Charger that has half wave rectification

and measure the voltage drop across the battery compare that to a similar battery (same total cranking Amps) . There's no substitute for a good deep discharge battery but I use the junk batteries that I've cleaned for a lot of things My favorite is a battery tool shop power . The wet cells make a nice addition to the shop . They are light and I put  four in the truck when I'm going to work. When I get home I have a fresh charge to work with

[Ungrounded Lightning Rod]

Two of the major failure modes of car batteries are:

 - Sulfation (high resistance, reduced capacity) and

 - High self-discharge from flaked-off plate material piling up at the bottom of the cells.

If your batteries are free you can get around partial sulfation (if it hasn't broken up or clogged the plates too badly) by just having a lot more batteries.  B-)

High self-discharge will cause the battery to discharge overnight, making it useless for storage.  But you can cure that by rinsing it out and installing fresh electrolyte.  (Ick!)  You end up with less than the original capacity, of course, but it's a working cell again.

Some other failure modes are more terminal - like a dendrite-shorted cell, heavy sulfation, or broken-up plates.  But those will show up as a battery that won't take a charge, or shows an extremely high charging voltage.

Car batteries, though, are NOT designed for deep-cycling and will break down rapidly (like in a few months) if you use them for that sort of application.  If you don't mind bringing home a new set of old batteries every couple months you'll do OK - at least until your area starts charging for disposal of old batteries.  B-(