I have found with my parallel wired 12V battery bank the multiple batteries in parallel will charge in the same amount of time as a single battery if all batteries are wired properly using the same lengths of cabling paths but you have to have a smart mode converter/charger unit that can produce 17-20AMPS of DC current per battery.
In the case of two batteries the size of the converter/charger unit should be a minimum of 45AMP DC output. Most of the single battery trailers usually have a 55 DC Output rated converter/charger.
Please post the brand and model of the converter/charger unit and the folks on here can tell you if that needs replaced if you want to re-charge the batteries from a 50% charge state to a 90% charge in around a three hour time frame. To get them to a 100% charge rate it will normally take around 12 hours of charge rate if the converter/charger is rated at 45AMPS or 55Amps. The camping off-grid idea is to start out with a 100% charge state battery bank and when the batteries drop to around the 50% charge state you will want to charge them back up to at least the 90% charge state which will take around three hours time. Then you can get almost full performance out of the batteries the next day/night run off the the two batteries again. You can do a good 12-14 of these 50% to 90% charge state before you must do a full 100% charge state. This of course will take a good 12hours of charging to get to a good 100% charge state. This is all battery science when using the stated standard DC VOLTAGEs that are picked by the battery folks designed to not boil out your battery fluids over the best timing they can do getting to the full 100% charge state.
If your converter/charger is only one of those smaller 30A DC OUTPUT units then it will take much longer to recharge the batteries.
Another issue might be to increase the wiring size from the converter/charger if it is small to a larger AWG size. I would suggest to use a 4AWG size wiring cable going from the converter/charger unit to the battery terminals.
This is also a great time to change out your internal lights from the incandescent type to LED type. This is a hugh savings in power consumption and getting the same amount of light. A typical incandescent automotive type light bulb will draw around 1AMP of DC current. The LED replacement unit for this light will only draw around .2 AMPS DC current. When you have some 12-14 of these lamp bulbs in the ceiling of your trailer this adds up big time...
Just food for thought - Confirm all of this with battery experts on here... I am just a self trained battery user with no formal battery training expertise and all of this is based on my personal experience using my 12V battery bank in my off-road camping conditions...
I have been using my three standard issue 85AH 12V Interstate batteries wired in parallel since 2009 and two of these batteries has finally got to the point of hold their good performance just last season.
Roy's image
These three batteries are wired in this fashion. Was originally four GP24 85AH batteries but I lost one due to over charging in the first month and the battery fluids boiled out.
Roy's image
My new battery bank in the planning stage now will look something like this drawing..
Roy's image
The new batteries will be mounted across the same trailer tongue position but will be using one of those Torklift battery boxes with slide off metal top.
Roy Ken
