Some topics take little research. A trusted friend, and electrical engineer went with AGM batteries. Although he travels on vacations only, has no solar and does not routinely boondock. From what I’m reading, how you plan to camp, travel and power up has a lot to do with the decision as to what batteries you go with.
I anticipated we would start off with two batteries (12 volt or 6 volt). For some reason if there is an option then I’d prefer 6 volt AGM golf cart type batteries from a reputable company. A blog reader suggested we just start off with two batteries and see what our electrical needs are before we invest in a permanent solution. After we travel for awhile, and maybe decide what solar system – if any- we are going with then look at batteries more closely. I’ll make sure our battery compartment can handle expansion.
Here are my notes:
- Good article from doityourself.com RV that describes the types, pros and cons.
- If you move from park to park with electrical service you will not need the same as if you boondock or have solar. Also pay attention to the maintenance requirements.
- Heavy-duty batteries designed for RV’s are called deep-cycle because they can be discharged and recharged more often and to a deeper discharge level than engine-starting batteries which allow for better cold cranking amps.
- Deep-cycle batteries come in three basic types: Conventional flooded electrolyte, gel type and absorbed glass mat (AGM). Flooded-type batteries have been around the longest, are most often supplied as original equipment and offer good capacity at the lowest cost. Flooded cells with removable caps require periodic checking and refilling with distilled water to maintain their electrolyte level. Batteries that get a fast charge, are used in hot weather and/or frequently cycled will use more water. If the electrolyte level drops below the top of the internal plates, the battery may be ruined. Flooded batteries require more frequent cleaning of corrosion from terminals. A sub-category of the flooded cell is the maintenance-free battery, which uses calcium mixed with the lead to reduce water usage. They usually have caps that can be removed if necessary, and if they are used hard (deep discharges and fast charging) they may need water added.
- Both gel and AGM batteries cost more than flooded cell batteries, usually last longer and don’t require maintenance. Instead of a liquid electrolyte like flooded cells use, gel-type batteries use a thick paste electrolyte that doesn’t require periodic refilling with water. However, gel cells don’t tolerate fast charging well. AGM batteries, which have their electrolyte absorbed in a fiberglass-type matting wrapped around the internal lead plates, also don’t require water, but can tolerate fast charging better than gel types.
- Deep-cycle batteries used in RVs typically come in 6- or 12-volt configurations. Six-volt batteries must be installed in pairs and wired in series (connected together so that a + terminal is connected to a – on the other side) so that their combined voltage will be a 12 volts that the trailer wiring requires. Twelve-volt batteries can also be used in pairs, but they must be wired in parallel (+ to + and – to -) so that their combined output remains at 12 volts. When 12-volt batteries are wired in parallel and used in pairs, the stronger one will discharge into the weaker one (known as cannibalizing), whereas a pair of 6-volt batteries in series won’t discharge each other. Don’t get confused, one twelve volt battery is not better than one six volt battery. Each may have the same amp hour rating. You just need the two six volt batteries to get the 12 volts that are required.
- Brands I’m reading about suggest Cosco and other box store batteries are all not the same. Trojan and Interstate are popular. Lifeline is also mentioned.
- Six volt “golf cart batteries” are wired in series to produce 12 volts. I’m reading a good setup for house batteries (ones used to power light and such compared to starting an engine) are good. With the best setup for boondocking being the AGM type.
- Have to establish what is the max amps per hour needed. Deep cycle battery capacity is measured in AH (Amp-Hours), meaning the total number of amps of power it can deliver in a 20 hour period. I’ve read not to run the batteries down more than 50% without a recharge. Some battery types, like AGM, can handle a faster recharge. Lithium batteries are newer technology and I understand they require unique recharging methods. Believe lithium battery is much less weight than others.Four
- Four six volt batteries weigh something like 300 pounds.
- Battery compartment size is going to dictate some of the selections. For example if your able to go with two six volt or two 12 volt which are shaped different.
- Short article by RV Doctor who recommends six volt.
- Another longer article with everything you would want to know about deep cycle batteries.
Here is a photo from the RVing With the Fergs Blog. It’s their solar system with four batteries in the basement. Had not thought about using the basement for extra batteries. Wonder if you have to do anything special for ventilation?
Found this chart to compare battery size codes and read about the T-105 six volt frequently being used:
U1 34 to 40 Amp hours 12 volts Group 24 70-85 Amp hours 12 volts Group 27 85-105 Amp hours 12 volts Group 31 95-125 Amp hours 12 volts 4-D 180-215 Amp hours 12 volts 8-D 225-255 Amp hours 12 volts Golf Cart & T-105 180 to 225 Amp hours 6 volts L-16, L16HC etc. 340 to 415 Amp hours 6 volts
I read up on charging systems for batteries, inverters and converters. I learned most RV’s come with a single stage charger which do very poorly at charging, taking hours. A multi-stage charger puts move amps to the battery when it’s low because it will except charging quicker with more amps. As it become closer to complete charge the battery charges more slowly, unless you have a multi-stage charger.