Batteries

Thanks for the replies. I thought it would be ok but I was not sure.

Eric

Myth, batteries connected together must be idetical.

Fact: This is true if the batteries are wired in SERIES, like GC-2's. to get a higher voltage, In this case they need to be the same make, model, size, and age, Puttign two different six volt batteries in series will cause problems, Example a 215 and a 230 amp hour, or a Flooded wet cell and an AGM.

Batteries in PARALLEL however, only need to be the same chemistery and voltage.

So you can indeed put a group 24 (About 75 amp hour) in parrallel with an Group 31 (130 amp hour) they will share in this case the smaller battery doing about 35 percent of the work and sucking 35 percent of the charging current (I rounded a bit) (you will notice it has about 35% of the total amp hours (205) as well.

Batteries in parallel are socialists, Each according to his abilities, each according to his needs.

But this only applies to PARALLEL hookups.

Also truly big difference parings, IE: Group 24 with a 4D or pair of GC-2) might not be a good idea for other reaons,, If a cell or two short in the smaller battery, the bigger one can blow it up (Small explosion, major pain in the clean up as acid sprays all over).

He should verify that won is week first.

Since you said that they are chassis batteries (SLI Starter Lights Ignition) it would depend on the specifications for that particular chassis, e.g. Freightliner, Spartan etc. Most chassis require a minimum CCA to be able to handle the engine pre-heat, glow plugs and other drains on the battery bank and still start the unit. In some cases they are wired in parallel so you still get 12VDC in other cases they are in series and you get 24VDC. If they are in series then you have more of a problem. You get the CCA of the weakest battery. I.e. you can add the voltage together but not the amps when you are running batteries in series. If the batteries are in parallel it and the lower of the two batteries is at or exceeds the minimum CCA for the coach then you will be fine. E.g. coach manufacturer requires 2 x 600 CCA batteries and you have one 600 CCA and one 700 CCA. That is no problem. If the coach manufacturer requires two 700 CCA batteries and you only have one, then you potentially have an issue.