Batteries again

[forestwalker]

Any advantage/disadvantage to connecting a group 24 to a group 27 ?
 Will it hurt anything ? We currently have two group 24's connected,but have a group 27 sitting in the garage.Will we gain any potential by switching to a 24/27 combo ?

[MtnCamper]

You will gain time, before the combo is dead. Only thing you need to watch for is, if the batteries are both in good shape, the good one will bleed off and feed the weak one, Then they will both discharge from there. It'll work, maybe not as well as 2 new 27's hooked together, but it will work.

[mike4947]

Forest, like Gary said the stronger will try to charge the weaker one. If you've been running the two group 24's in parallel, most likely you won't see much extra adding the group 27 in place of one of them, due to the drain you'll see between two different aged batteries.

You could go to a single hook up and switch between them. That would give you the extra capacity between a group 24 and a group 27, That would also keep the weaker of the two from boiling when charging them as a pair as well.
 
Check the RC's on the batteries and as a good estimate of "useable amps till 50% disharged" is dividing the reserve capacity by 2.4 you can find out just how much extra you could theoretically get by using the group 27 rather than one of the group 24's.

[Tim5055]

OK, I'm going to be the voice with a differnet opinion here.

I violate the rule on mis-matched batteries. I carry both a group 24 and a group 27, but only when dry camping. The only way I can see that one battery will try to charge the other is if you connect a discharged battery to a charged battery. Just like water seeking it's level, the charged battery will try to charge the weaker one.

I have read almost every battery web site I can find. The only caution about mis-matched batteries I could find dealt with charging them. If you charge them connected together, either the group 27 will not fully charge or the group 24 will over charge. For this reason I charge them individually (not connected together) with a quality charger in the garage before and after every trip. With both at 12.7 volts, connecting them together will not cause a mis-match.

The trickle charge from the tow vehicle is so little I don't worry about it.

When camping at sites with electric, I only connect one battery.

Simple Rules

1. NEVER connect a discharged battery to a charged one.

2. Charge each battery individually using a quality charger, not your pop up converter before your dry camping trip.

3. Connect the batteries together in parallel while fully charged and use them together as a "single battery".

4. Charge each battery individually using a quality charger, not your pop up converter after your dry camping trip. Never store a battery in a discharged state.

[mike4947]

Tim, mismatch isn't due to size, but age or type. A 2 year old battery hooked to a new battery will have a lower potential fully charged voltage and will draw down the newer higher potential voltage battery.
Simalarly say a wet cell deep cycle and AGM type battery will also tend to try and charge the lower potential battery.
So even seperating them for charging still limits you to twice the lower batteries potenial limit.

You rules work well except the paralleling two batteries. Then they should be the same type and similar in age and lfe experience.
 
If batteries are used in parallel (providing the above is followed) they should be charged in parallel, all the battery manufacturers agree on that one.

[deniski]

not sure whether or not to start a different thread?  BUT, how would I know a "quality charger" (quoted from above) if I saw one?  I've been looking at one at Walmart that supposedly quits charging once the battery is fully charged...which is something we need after the last battery we killed....

[Tim5055]

Tim, mismatch isn't due to size, but age or type. A 2 year old battery hooked to a new battery will have a lower potential fully charged voltage and will draw down the newer higher potential voltage battery.
Simalarly say a wet cell deep cycle and AGM type battery will also tend to try and charge the lower potential battery.
So even seperating them for charging still limits you to twice the lower batteries potenial limit.

You rules work well except the paralleling two batteries. Then they should be the same type and similar in age and lfe experience.
 
If batteries are used in parallel (providing the above is followed) they should be charged in parallel, all the battery manufacturers agree on that one.

Sorry Mike, you and I are going to have to agree to disagree.

I have used mismatched batteries (age and size) for  two years now.  I have never had a problem.  I charged them fully before camping.  I connected them together and use them as a singe "battery unit".  I always hd more then double the group 24 batteries limit.

I guess this is something folks have to figure out for themselves.

[aw738]

All this talk of using two batteries made me think of something. This might be obvious and redundant but I thought someone should mention it if it hasn't been said already. NEVER wire your batteries in series like they are in a flashlight. Doing this will double the voltage and not the amperage. The electrical system is designed for 12 volts only not 24. The correct wiring is positive to positive and negative to negative. Any of you diesel truck owners should have a good example of how to wire two batteries. If anyone is still needing an example find a friend that owns a diesel truck and ask to look at there batteries.

[mike4947]

AW, make that never wire your 12 VOLT batteries in series. 6 volt batteries do need to be wired in series to get 12 volts.
 
Tim, I'm glad it works for you. My posts just reflect what I've learned the hard way and what I've been taught over the years. Every rule has exceptions and I'm glad you haven't had problems.