Originally Posted by Neverhome
I went to my local auto parts store today for a replacement battery for my Montana. Requested a deep cycle battery and was steered to a Marine battery which they said was a deep cycle. Battery clearly stated starting battery, not deep cycle. Are all marine batteries deep cycle and is a deep cycle the best battery for an RV? Is there any problem using an AGM battery? I had heard they cannot be charged by a standard battery charging unit and I wonder if that includes the recharger in a camper.
The subject of batteries is truly wide and deep. There is no one, simple or easy answer that can be applied to all situations.
Generally, for the coach section of a motorhome a deep cycle battery such as a lead-acid marine battery is a better choice than a starting battery and if you wish to avoid getting involved in researching and developing an in-depth understanding of batteries and charging them, a deep cycle marine battery will probably suffice just fine in most cases. Starting batteries are meant to deliver large amounts of current for short periods of time whereas deep cycle batteries are meant to deliver lower amounts of power over longer periods of time and are therefore more appropriate for use in the coach section of an RV.
There are several types of battery technologies including lead-acid, AGM, and lithium. Each has its own characteristics as well as its advantages and disadvantages.
For a rig that gets only occasional light use it may be the case that almost any battery will do even a starting battery. However, it is best to understand what demands you will place on a battery before deciding which kind to get. There is no one answer that is right for everybody. You should also be cognizant of the features of your rig's charging system to make sure it is compatible with a battery you select. It is almost certainly the case that virtually every rig's charging system is designed to charge lead acid batteries.
When shopping for a battery realize that a very large percentage of batteries sold under various brand names such as Sears Die Hard, Interstate, etc. are manufactured by the same company, Johnson Controls. This doesn't mean the batteries are identical because they may be made to different specifications for different brand names.
Selecting a battery with a greater reserve capacity or ampere hour rating will provide more electricity and be usable for longer periods before recharging becomes necessary. Note, however, that even here making a choice isn't so easy. You see, there are different methods by which the ampere hour ratings of a battery may be determined and comparing batteries rated using one method to batteries rated using another method may result in a misinformed purchasing decision. I've written about this on my blog. Here is an excerpt: "Manufacturers and resellers of batteries use different methods to determine and advertise the AH capacities of their batteries and this must be understood in order to make an informed choice when selecting batteries. Using one method versus another can lead a consumer to purchase Battery One over Battery Two thinking he/she is getting more storage capacity from Battery One when in fact it’s the other way around. As it turns out, if you drain a battery more slowly, for example at 1 amp per hour, you will get more AHs out of it than you will if you drain it at a higher rate such as 20 or 25 amps per hour. A battery rated at 100 AHs using the 1 amp per hour rate of drain as a measure will likely have closer to a 75 or 85 AH rating if drained at 20 amps per hour. Manufacturers that want to make their batteries look good use the 1 AH numbers in their literature whereas a more commonly used industry standard is the 20 AH rate of drain. When comparing battery AH storage capacities you must have information expressed at the same rate of draw. When you hear that a battery’s AH rating at C1 is 75 it means that its Capacity is 75 AH when it is drained at 1 amp per hour. If a battery has a 75 AH capacity at C20 it means its AH capacity is 75 if drained at 20 amps per hour. Make sure that when comparing batteries you get their AH ratings at the same rate of drain, the same C rating."
If you want to keep things really simple just buy a deep cycle battery of the right group to match your battery box ("group" specifies dimensions). If you're trying to decide between two virtually identical batteries pick the one that weighs more. It is probably better made.