RV Battery Types - The Basics

[markopolo]

RV Battery Type Basics

Some quick notes on Lead Acid batteries commonly used in RV's. This information comes from a wide variety of sources and is my interpretation of the information I have read over the years. Questions, comments, corrections and discussion are welcomed.

Three types of batteries commonly seen on store shelves:
1. Starting batteries - intended for short, intense loads like starting the RV engine.
2. Deep Cycle batteries - intended for long term, less intense loads such as powering the lights, fans & pumps inside your RV.
3. Dual Purpose or Marine - these fall somewhere in between Starting and Deep Cycle batteries.

Two construction types of batteries commonly used in RV's. (Gel cell batteries ignored for this topic)
1. Wet Cell / Flooded - usually with removable cell caps to add water lost through electrolysis as needed for maintenance. This type of battery can be sealed "maintenance free" but more often those are Starting type batteries.
2. AGM - (Absorbed Glass Mat) sealed from maintenance (cannot add water). The electrolyte is gelled and suspended in a fiberglass mesh between and around the lead plates.

Generally speaking:
AGM batteries can be recharged quicker than Wet Cell / Flooded batteries.
AGM batteries cost more to purchase than Wet Cell / Flooded batteries.
Wet Cell / Flooded batteries tolerate overcharging better than AGM batteries.
AGM batteries vent less hydrogen gas making them more suitable for mounting inside an RV. Ideally, they will still be vented to the outside of the RV.
AGM batteries can be discharged at a higher rate than Flooded batteries which is useful if needed for large loads.
Wet Cell / Flooded batteries SOC (State of Charge) can be accurately determined using a hydrometer for specific gravity testing. This is not possible on sealed batteries.
Wet Cell / Flooded batteries require more maintenance; checking electrolyte level, adding distilled water when needed.
Wet Cell / Flooded batteries offer a better chance of recovery from damage cause by over-discharge or the result of chronic undercharging.

Battery capacity ratings:
1. CCA - Cold Cranking Amps - indication the battery is a Starting or Dual Purpose battery.
2. CA - Cranking Amps - indication the battery is a Starting or Dual Purpose battery.
3. RC - Reserve Capacity - how long a fully-charged battery can deliver 25 amps of current at 80°F before the battery is discharged down to 10.5 volts.
4. Amp Hour / Ampere Hour / Ah - typically expressed using the 20hr rate and would indicate the amps that can be delivered continuously while the battery is discharged down to 10.5 volts over a 20 hour period.

Th Ah / Amp Hour rating is useful for RV'ers to determine which battery has the greater capacity when shopping for a battery for RV systems use such as powering lights, pumps and fans etc. A battery with a higher Ah rating has a greater storage capacity. When comparing batteries, make sure compare the same Ah ratings. Do not compare the 100hr rating of one battery to the 20hr rating of another battery for example.

[booster]

Very well done, good information. May want to add to the "generally speaking" section that the AGMs will also discharge at a higher rate than wet cells making them better for the big inverter applications we are starting to see more of. Also could note that wet cells can be more easily monitored for SOC and deterioration, and can often be recovered from damage, but require regular maintenance.

[markopolo]

Thanks Booster. I updated the post.
I was going to add "Wet Cell / Flooded batteries offer a better chance of recovery from damage." but need to be more specific. How about "Wet Cell / Flooded batteries offer a better chance of recovery from damage cause by over-discharge."

[booster]

Originally Posted by markopolo

Thanks Booster. I updated the post.
I was going to add "Wet Cell / Flooded batteries offer a better chance of recovery from damage." but need to be more specific. How about "Wet Cell / Flooded batteries offer a better chance of recovery from damage cause by over-discharge."

How about "from over-discharge or chronic undercharging" ?

[markopolo]

Done.

Just a note: I excluded gel cells only because I often see low maximum charging voltages specified for that type of battery. Sometimes it's 13.80v for example. That makes it problematic for use in a vehicle if charging via the alternator if you also have wet cell or AGM under the hood as your starting battery. Some Gel cell battery brands specify a higher charging voltage.