Battery Balance

[JamesTimm]

Hi! I concidered posting this on one of the other, more lively, TC forums but I'm wanting to avoid a flame war. Simple questions over there sometimes lead to nasty exchanges. I have read several places that all batteries on the same circuit should be similar in both size and age. My question is: my TC's deep cycle battery and the truck's starting battery are sharing the same alternator while charging through a solenoid. Is this going to shorten the life of one or both batteries? If so, which should fail first? Thanks!

[BryanL]

You won't shorten the life any in normal use.

The reason for the recommendation to keep batteries in a bank similar is more for overall performance than anything else. As they are all used and maintained the same way, they all age the same and that means they all contribute a fair share to what you can get out of the bank.

If the batteries are unequal size or age then you won't have the same performance you'd get if they were all in top shape. The newest or biggest battery will be doing most of the work and that tends to age it a bit faster, depending upon use profile.

The biggest issue is to keep the chemistry and type the same. Here, the chemistry is lead acid and the type is wet cell. Most lead acid batteries have very similar charging voltage requirements so open and sealed automotive and rv batteries work well together. AGM's are very close but have a few quirks. Gel Cells need special attention

and here, you are only sharing charging, not use, so the battery bank similar thingy isn't the issue, only the charging voltages.

[JamesTimm]

It makes perfect since to me how that works now. They may be charging togeather but once the ignition key is turned off they become individual systems.
Thank you very much for clearing that up for me.
Jim

[wa8yxm]

THe rule I give is that all batteries should be the same VOLTAGE if in parallel, and if in series then it's a bit more complex (Same capacity)

I also preach that you should treat batteries in series not as batteries (Which they are electronically not) but as Battery (Singular) which electronically they are. A collection of cells.

So if batteries are wired in series (Six volt golf car batteries) then you can easily answer your questions by thinking like this:

Do they need to be the same, make, model, age, capicity, type. and so on?

Would you buy a single 12 volt battery that was half one thing and half another (IE: half new, half old, Half, Flooded, Half AGM?) They need to be the same.

Now, when you start paralleling batteries do they need to be the same?

Answer: Not so much.. Though different types (Flooded wet, Maintenance Free wet, AGM, PbCa, and so on) all have slightly different voltages and even different makes of the same battery may be different voltage wise.. Thus mixing types and brands may not be the best idea

As for size.. What happens when you parallel say a G-24 with a G-31.. Some folks will tell you that "Well the smaller battery will charge up and signal the converter "All charged" and the larger one will never fully charge" This is. of course, Male Bovine Produced Organic Ferterlizer. (BS).

What will happen is the two batteries will share the charging current acording to their capacity (About 40/60 percent or there about) when charging and will reach full charge at exactly the same instant.. Likewise when loaded down they will provide current in the exact same purportion so they will both discharge to exactly the same level.. It can be no other way less you use very small wires to hook 'em up.

And in that lies the key

If the house is wired with say #8 from the battery to the fuse block,, Use at least #4 battery to battery.

[JamesTimm]

Thanks for the reply. That is a best explination I've heard so far discribing multible TC batteries as a single use set. Also its good to know that both the truck's and TC's batteries will become fully charged using the truck's alternator. I am using two 14 foot 4 guage wires between the batteries.
Thanks Again,
Jim

[Paul R. Haller]

Originally Posted by JamesTimm

Thanks for the reply. That is a best explination I've heard so far discribing multible TC batteries as a single use set. Also its good to know that both the truck's and TC's batteries will become fully charged using the truck's alternator. I am using two 14 foot 4 guage wires between the batteries.
Thanks Again,
Jim

I do not like losing battery voltage to my wiring. In my trailer all grounds battery inter connections and leads are wired with 4/0 welding wire with crimped heavy duty lugs. If you are using an inverter use 4/0 from the battery string to the inverter not longer then about 18 inches long. I have a 3000 watt inverter and to run even your microwave for 5 minutes you will be drawing out about 250 amps for 5 minutes straight out of your batteries to the inverter. With small wiring or bad connections 250 amps can easily start a fire plus you are just wasting potential from your batteries. My first trailer had 4 Trojan 6 volt batteries wired in series to create 2 12 volt banks in parallel. All my connections were wired using # 2 wire and the leads were about 8 feet long with soldered connectors. When running the inverter to use my microwave, I measured a .93 volt drop from the wires over that 8 foot length. My inverter would start beeping with a low voltage warning as soon as the microwave was turned on with new and topped off batteries. How could this be? After rethinking my design I decided to use larger wires and move the inverter to within 24 inches of the batteries. It took me a whole day to get the wire, cut it and crimp the connections, build the brackets, and wire up the inverter. Working with 4/0 wire is like working with water pipe it's so heavy. At the end of the day I was completely pooped out. I remeasured my voltage drop under load.with the new wires and configuration. My voltage loss across the wires droped to .003 volts.under load. WOW, now even at drawing 400+ amps at full output I never got a low voltage warning.and can use all the power I want from my batteries for short bursts. Remember that voltage loss from wiring just throws away all the potential that you created using good batteries and equipment. No matter how good all that stuff is, with undersized wiring you'll never realize any of it.
-Paul R. Haller

[Ray,IN]

Welcome to Battery University has all the information one would ever need to know about batteries. Multiple batteries in the same bank should be of the same age, capacity, and condition. The weakest battery will draw down the others, shortening their lifespan. It's all in the link.