Do coach batteries all need to be the same type?

[acenjason]

OK, I want to add another battery to my 75 Brave. I already have one coach battery.  I have a duel purpose Rv/marine battery. I know it isnt a deep cycle but It was a gift and I'm on a budget. So, my question is should I buy a matching duel purpose battery? I think I read somewhere that all the batteries in the coach battery pack should match. Is this true? Or would it be OK to just go buy a huge deep cycle so I have a lot of amp hours? I have tried to look on the search and have got mixed messages. Can anyone help a Winny jockey out?

[LJ-TJ]

Boy did you open a can of worms. I was thinking the same thing and ended up buying two used Trojan 6 volt T-105 batteries.  Got them for the cost of 1 good deep cycle battery. I let you knno how it works out as we are gong boon docking this weekend Friday to Sunday. They say I should be able to run everything for the weekend off these two batteries. I'll let you know how it works for me. Keeping my fingers crossed. The only way I'll be able to recharge the batteries is off the alternator when I'm driving around during the day.

[circleD]

Yes you need to have matching amperage and capacity on your batteries or you start a small energy battle between them. Will 2 different batteries work? YES. Will they last long? Not as long. It'll also cause charging issues.

[DaveVA78Chieftain]

This mostly has to do with the thickness, construction, a quantity of the lead plates inside the battery. 

The chassis starting battery uses many thin honeycomb lead plates that allow high current for starting and quick recharge in exchange for lower total amp hours.

The RV/Marine combo battery has fewer but thicker lead plates which provide starter current for the smaller outboard motor engine.  The thicker plates provide a higher amp hour value.

A true deep cycle has the thickest plates which are designed to provide a constant current draw for a long period of time resulting in higher amp hour ratings.

These design differences result in different AH ratings as well as different charging times.  That is the reason it is best to match type to type when wired in parallel for the purpose of increasing total AH.  This also prevents one battery pulling down the other because of design differences.

One may ask why then is it OK to gang chassis and coach battery banks using the DUAL/NORM/MOM switch (isolation relay)?.   For starting, this is only intended to be used for a short period occasionally (e.g emergency) which is not excessive enough to create damage to either battery.   For charging, it is normally just on occasion and you are not using this mode to discharge the battery.

Dave

[DaveVA78Chieftain]

TJ - purchase an inexpensive small 2 cycle generator to recharge the batteries with your converter.  Oh, get that converter upgrade done so your not limited to just a few charging amps.  A 3 stage 45 amp converter only draws around 600W so a small 1000W generator can be used to restore power.   And in bulk mode, most all that 45 amps will be used for battery charging.  The 1000W genny is just not big enough for doing much else at the same time, maybe a laptop.

Dave