More questions on enlarging battery bank

[rich85704]

Trying to enlarge the battery capacity on my Class C.

My thanks for the responses to a query I posted a few days back on what battery types might be safe inside a coach. The consensus was, pretty much, AGM -- with a few cautious souls warning that even AGM batteries can vent under certain circumstances.

I thought I'd found a way to sidestep the whole issue by replacing the existing two flooded batteries (approx 60 Ah each) with two 100 Ah batteries (from Renogy) Gotcha! The existing batteries are one physical size (Group 24), and the new ones would be so much bigger(Group 30) that there's no way they (or any other 100 Ah battery) would fit.

So my latest idea is to put a third battery in a storage compartment right next to the existing batteries. The cable run would be perhaps 3 feet; the existing batteries are wired in parallel with cable which is (I think) 6awg and less than 12" in length.

The questions:

-- what gauge cables should I use for this run? Should I use 6awg cables to match the existing jumpers, or 4awg because the cable run is significantly longer?

-- can I run a new 100Ah AGM battery in parallel with two 60Ah flooded batteries?

-- The storage compartment where the new battery would live is underneath the coach area, running crosswise the length of the coach, with doors at each end. Would putting an AGM battery in this space pose any risks in the coach space above?

Thanks, again, folks!

Rich

[theoldwizard1]

time2roll wrote:

rich85704 wrote:
-- can I run a new 100Ah AGM battery in parallel with two 60Ah flooded batteries?

I do not recommend it. AGM and flooded charge at different speeds and have very different (in the battery world) resting voltages. You will not really get the full added capacity you expect and the life will be shortened.

Best to go all AGM or all flooded.

CONCUR !

[time2roll]

rich85704 wrote:
-- can I run a new 100Ah AGM battery in parallel with two 60Ah flooded batteries?

I do not recommend it. AGM and flooded charge at different speeds and have very different (in the battery world) resting voltages. You will not really get the full added capacity you expect and the life will be shortened.

Best to go all AGM or all flooded.

[corvettekent]

I would use 4 gauge because it much more common and easy to find.

I can tell you when I enlarged my battery capacity I used four 6 volt flooded acid batteries and used a vent hose kit to vent outside. I works very well and maintenance is very easy.

[Sam_Spade]

rich85704 wrote:

-- can I run a new 100Ah AGM battery in parallel with two 60Ah flooded batteries?

CAN you....yes.
SHOULD you.....NO.
They have different charging characteristics.

Multiple batteries in parallel really isn't the best solution because eventually one will become weak first and draw more than it's share of the charging current......causing the others to slowly go bad too.

Have you researched size limitations with two 6 volt AGMs in series ??

[wa8yxm]

There are some new battery types (https://bioennopower.com/) that look very interesting.. But AGM is what I'd use. inside or.. Alternative

JC Whitney (if I spelled it properly) used to sell a VENTED battery box.. Now I got one, but did not like it as well as I might So here is a suggestion.

Build a box Air tight (use a screw down lid with weather stripping)

In the bottom of the box drill a hole and seal it to a piece of PVC pipe at least 1-2 inches down through the floor (Set it on a flange fitting)

Likewise put a vent in the side of the RV connected to the box so air can come in via the floor and out the side.. now if it vents.. it vents, but NOT into the RV (Seal where the wires go in/out with GOOP)

[Chuck_thehammer]

my opinion

mixed size, type, age does not go well (long term)

if multi-able batteries... main power (charge) at one end... and ground at other end.... and all being in parallel..

if bad connection ... power or ground.. all does not charge or discharge.
else one has what it needs. and all/most others go DEAD.
not so easy to explain..
I have been setting up multi batteries in cars/trucks since the late 1960s, for work use.

[jplante4]

I'm not sure if this chart is for AC o DC or if it even makes a difference.



Mixing battery types and sizes usually causes problems. One in the bank will usually grab the charge and the others will starve. If you do, then I would isolate the 2 different types with a battery switch (the kind in boats with OFF/1/2/BOTH positions) and switch to the bank you want to charge. This would apply to newer vs older batteries as well.