Combining battery sizes in parallel.

I wouldn't mix the batteries, but you could get two charge controllers and have two solar systems (many options here), or you could set up a marine battery switch so you could charge the Trojans and then when they are full, use the switch to charge the other batteries.

We camp alot off-grid using our batteries. Can do alot of things every day but by 8AM the next morning will want to recharge my batteries from their 50% charge state back up to the 90% charge state so we can do all of this all over again for the next day/night battery run.

I haven't gone with solar yet but having my small 2KW generator around is a must have item for me. It works rain or shine and even on cloudy days for sure haha...

With my setup and small area for solar panels I probably would only get a solar benefit of reducing my use of the small generator down to perhaps one hour a day verses the three hour run to get past the 50AMPS plus DC charging current demand of the batteries for the initial re-charge procedure. Then the solar panels could continue giving me the batteries charge demand of 6-8AMPs for remaining of high sun for the day perhaps...

Not having a generator around would not be a good idea in my setup. Got to have a good PLAN B here...

My new battery bank I am working on will be two groups of 6VDC Trojans GC2 batteries in series to give me around 480AHs capacity...

I too have not had good luck charging different batteries at the same time using the same charger. What I do here is use the on-board converter/charger PD9260C 60AMP Smart mode unit for the main battery group and then use my portable B&D VEC1093DBD 40AMP smart mode charger for the external batteries I sometimes carry with me for backup.

Roy Ken

dms1 wrote:
I wouldn't mix the batteries,

I wouldn't either.
And I definitely wouldn't do without a generator.

I'll be interested to see how this turns out.

I also wouldn't mix sizes and ages of batteries

I worked for a large inverter manufacturer for 8 years, which is one of the companies that got swallowed up by Xantrex. We ALWAYS recommended not mixing battery types, size and ages in a battery bank.

Well, if you didn't want to start a debate you shouldn't have posted, because this subject inevitably starts a debate.

Ideally, you should not mix battery sizes, at least on a long term basis.

Electrically it will work fine but over a period of time the differences between the batteries could cause problems. Weak batteries will kill good batteries for sure.

I've been using different battery banks in parallel for years. One bank in my truck and another in the trailer. When I'm drawing power for the camper they are connected. When I get home I disconnect from the trailer and park the camper in the barn, so they are never connected long-term.

I know all the doom and gloom warnings, but let me give you a bit of practical experience. We had a 2008 Allegro Bus with 4 flooded 6v batteries as house batteries. Since we boondock a lot, I wanted something better. I split the DC bus and added a forward inverter so the high draw items like satellite TV, satellite Internet and Entertainment center were on the front system. I then put 4 AGM 6v batteries in the main house battery bank and moved the 4 flooded batteries to a newly constructed rack under the front cap to feed the forward AC inverter. In order to keep all batteries charged I set up a power relay that allowed me to parallel both sets of batteries so they could be charged from shore power, the generator or the engine generator when the Bus engine was running. This relay also allowed us to use all 8 batteries to power all DC items on the RV. That setup worked just fine for over 2 years and with heavy use.

Again, this setup was against all "accepted" reasoning and recommendations I could find. My suggestion to you.... Try it and see if it works for what you want to do. What "EVERYONE" knows and what works are sometimes very different.

why not just put another 2 Trojan T-105 RE's in the OEM battery location?

This is done every day in the commercial world. I would separate them into two banks and charge them together but use and store them separately. For best efficiency, I would only connect them all together when charging.

pigman1 wrote:

Again, this setup was against all "accepted" reasoning and recommendations I could find. My suggestion to you.... Try it and see if it works for what you want to do. What "EVERYONE" knows and what works are sometimes very different.

And what can be explained by pure dumb luck often is passed off as "practical experience". :)

What you did is quite different than just paralleling two sets of dis-similar batteries full time.

Just dismissing the "conventional wisdom" and running off on your own sometimes works out OK......but more often you find out WHY everyone said what they did. And the lesson is sometimes costly.

Running two charge controllers off the same bank of solar panels would help with optimally restoring your batteries. Since they will be different capacity, you do not want to gang them together. However, you could run them on isolated circuits - Perhaps one bank does nothing but powers an inverter while the other powers the camper DC draws.