connecting old & new batteries in pllel ok?
 

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.

Thanks!

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.

There is a time to pinch pennies and a time not to pinch pennies.

This is not a time to pinch pennies. Trash the old battery and get a
new one.

All the best,

Tom
--------------

"What the hell's the deal with this newsgroup...
is there a computer terminal in the day room of
some looney bin somewhere?"

Bilgeman - circa 2004

Ok.. but can you back that up with some reasoning or is that just a random
statement?


There is a time to pinch pennies and a time not to pinch pennies.

This is not a time to pinch pennies. Trash the old battery and get a
new one.

All the best,

Tom
--------------

"What the hell's the deal with this newsgroup...
is there a computer terminal in the day room of
some looney bin somewhere?"

Bilgeman - circa 2004

There is a time to pinch pennies and a time not to pinch pennies.

This is not a time to pinch pennies. Trash the old battery and get a
new one.

All the best,

Tom
--------------

"What the hell's the deal with this newsgroup...
is there a computer terminal in the day room of
some looney bin somewhere?"

Bilgeman - circa 2004

I agree you need to trash the old one or put it in something else. You need
to have similar batteries if you are going to hook them in Parallel.

" Ok.. but can you back that up with some reasoning or is that just a random
statement?

Yea it is called Internal Resistance.

There is a time to pinch pennies and a time not to pinch pennies.

This is not a time to pinch pennies. Trash the old battery and get a
new one.

All the best,

Tom
--------------

"What the hell's the deal with this newsgroup...
is there a computer terminal in the day room of
some looney bin somewhere?"

Bilgeman - circa 2004

On Thu, 28 Oct 2004 23:44:30 GMT, "Falky foo"
wrote:

Ok.. but can you back that up with some reasoning or is that just a random
statement?

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.

It is also unlikely that you will be able to build a giant amperage
battery using an old battery in parallel with a new one. There are
established reasons for not doing this having to do with cell
resistance and the amount of lead, zinc and acid left in the old
battery after a few years of use or abuse. You could also make a case
for unbalanced load, but that's a little esoteric.

Probably the safest thing to do is to take it to a local mechanic and
have the battery load tested with a real load tester - one that places
a heavy load on the battery. If it's good, then you win. If it's
not, then you know for sure.

For my money, any old battery is immediately suspect if it holds a
charge or not and is changed regardless.

I apologize for the pennies comment, but the central concept still
holds.

Take care.

Tom

"The beatings will stop when morale improves."
E. Teach, 1717

Ok sounds good. thanks for the thorough explanation.


"Short Wave Sportfishing" wrote in message
...
On Thu, 28 Oct 2004 23:44:30 GMT, "Falky foo"
wrote:

Ok.. but can you back that up with some reasoning or is that just a
random
statement?

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.

It is also unlikely that you will be able to build a giant amperage
battery using an old battery in parallel with a new one. There are
established reasons for not doing this having to do with cell
resistance and the amount of lead, zinc and acid left in the old
battery after a few years of use or abuse. You could also make a case
for unbalanced load, but that's a little esoteric.

Probably the safest thing to do is to take it to a local mechanic and
have the battery load tested with a real load tester - one that places
a heavy load on the battery. If it's good, then you win. If it's
not, then you know for sure.

For my money, any old battery is immediately suspect if it holds a
charge or not and is changed regardless.

I apologize for the pennies comment, but the central concept still
holds.

Take care.

Tom

"The beatings will stop when morale improves."
E. Teach, 1717

Right, but he didn't say that in his original post, which is why I asked
whether it was a random comment.

Batteries in the same circuit should always be of the same type, brand,
size and
age. Nothing random about it. This applies to everything from flashlights
to
space shuttles.

BB


There is a time to pinch pennies and a time not to pinch pennies.

This is not a time to pinch pennies. Trash the old battery and get a
new one.

All the best,

Tom
--------------

On Fri, 29 Oct 2004 00:00:55 GMT, wrote:

On Thu, 28 Oct 2004 23:44:30 GMT, "Falky foo"
wrote:

Ok.. but can you back that up with some reasoning or is that just a random
statement?

Batteries in the same circuit should always be of the same type, brand, size and
age. Nothing random about it. This applies to everything from flashlights to
space shuttles.

In one of my previous lives, I wired two different six volt batteries
to make a twelve volt source for starting a International Super M
tractor. :)

I've also jury rigged a Maglite that used D cells with a C cell (I was
short one D battery).

Take care.

Tom

"The beatings will stop when morale improves."
E. Teach, 1717

On Thu, 28 Oct 2004 23:39:41 GMT, Short Wave Sportfishing
wrote:

This is not a time to pinch pennies. Trash the old battery and get a
new one.

=================

Yep, no question.