battery charging question

[handfixer]

I have been reading the recommendations to link two batteries in series or parallel.  I am wondering if I do that, should I charge both batteries at the same time or charge them separately? Any recommendation for good smart charger?

[wavery]

I have been reading the recommendations to link two batteries in series or parallel.  I am wondering if I do that, should I charge both batteries at the same time or charge them separately? Any recommendation for good smart charger?

It is "best" to charge them separately. Charging them together is OK if both of the batteries are new and in perfect condition. Assuming perfection is always risky business though. :sombraro:

When we are at home, I charge ours separately. If I charge them while camping, I just charge them hooked together.

[dthurk]

If you have 6 volt batteries, link them in series.  If 12 volt, link them parallel.  Which to use causes some amount of discussion, there are pros and cons to each.  We have 2 6 volt batteries mounted on the tongue and charge them as they sit, wired together in series.

[mike4947]

All the battery manufactures agree to charge multiple batteries the way you use them. If they are connected during use charge them that way; and if used separately charge them separately.

[tlhdoc]

You can charge them together.

[wavery]

Here's the issue with charging 2 batteries, hooked together.

If one battery is weaker than the other (lower specific gravity in one or more cells), the lower battery will demand a charge when the better battery is already fully charged. If you leave the charger on for days at a time, the batteries may prematurely run out of water and cause damage.

Also, if you leave the batteries tied together while storing, a weaker battery will tend to draw down the stronger battery as they will continually try to equalize. This will increase the # of cycles on a good batter, over time.

Now, having said all that, keep in mind that every battery is made up of a number of 2v cells. Each of those 2v cells is a separate battery in it's own right. All of those cells are wired together in series. In the case of a 12v battery, it's really 6 - 2v batteries. So, when you charge your 12v battery, you are actually charging 6, 2v batteries that are tied together.

As you well know, if one cell goes bad in any 12v battery it drags the entire battery down over time and often times you will find that 2 or more cells will fail concurrently. If you leave 2 batteries wired together, you spread that risk over both batteries.

If you have a hydrometer and check the specific gravity (and water level) in your batteries from time to time and determine that all cells are fairly equal, there is no risk in charging the batteries together. The "risk" increases when you don't know what you have.

[handfixer]

Here's the issue with charging 2 batteries, hooked together.

If one battery is weaker than the other (lower specific gravity in one or more cells), the lower battery will demand a charge when the better battery is already fully charged. If you leave the charger on for days at a time, the batteries may prematurely run out of water and cause damage.

Also, if you leave the batteries tied together while storing, a weaker battery will tend to draw down the stronger battery as they will continually try to equalize. This will increase the # of cycles on a good batter, over time.

Now, having said all that, keep in mind that every battery is made up of a number of 2v cells. Each of those 2v cells is a separate battery in it's own right. All of those cells are wired together in series. In the case of a 12v battery, it's really 6 - 2v batteries. So, when you charge your 12v battery, you are actually charging 6, 2v batteries that are tied together.

As you well know, if one cell goes bad in any 12v battery it drags the entire battery down over time and often times you will find that 2 or more cells will fail concurrently. If you leave 2 batteries wired together, you spread that risk over both batteries.

If you have a hydrometer and check the specific gravity (and water level) in your batteries from time to time and determine that all cells are fairly equal, there is no risk in charging the batteries together. The "risk" increases when you don't know what you have.

Thank you everybody for you input.