On Thu, 28 Oct 2004 23:35:15 GMT, "Falky foo"
wrote:

Hi, just got a boat that came with an old, run-down 12v battery. I tried
charging it fast and my charger said "fault." Then I charged it slow and it
apparently charged ok. I topped off the water inside. It's 70 Ah, Series
24. I also have a new battery (105 Ah, Series 27) but I'd hate to trash the
old one in case it's still useful.

Can I wire them in parallel to add the currents and have essentially one
monster 175 Ah battery? Or will the old one somehow screw up the new one?
If I can, which should be on the 'outside' and which on the 'inside' of the
circuit, or does it matter? I'd rather not have to switch between them, and
I'd rather not throw out the old unless I have to.

It is generally recommended that all parallelled batteries should be
of the same vintage and usage history - however, I don't think you'll
damage either battery by using this mismatched set. I would suggest
you occasionally try each battery alone, just to see if it still
works.

I've used mismatched batteries a couple of times, and when I tried
them individually after a while, was surprised to find that one was
totally dead, so the newer battery was doing all the work.

Batteries are not expensive - since your Group 24 battery showed
"fault" on one charger, I'd probably recommend replacing it.



--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Short Wave Sportfishing wrote:



What I am essentially saying is that if the battery is old and was
allowed to discharge such that your charger said fault, then the
chances are, and without the ability to load test the battery from a
remote location, that the battery is probably junk. I can slow
charge a battery also - doesn't mean that the battery has the ability
to hold that charge.


100% agree that Falky foo should get a new battery and forget about
trying to parallel two unlike batteries, however I'd like to add this
little tidbit of experience.

I bought a portable smart charger manufactured by Vector. It has
selectable charging rates of 2, 10, 20 and 40 amperes. If you try to
charge a small battery at the 40 amp setting, the Vector will shut down
and display a fault condition, even if the battery is perfectly fine.
The smaller batteries have to be charged at a lower setting using this
type of charger.

Eisboch