2nd battery

There are virtually no true deep cycle wet cell 12V batteries. If you want true deep cycle performance switch over to 6V golf cart batteries. They are inexpensive and widely available.

Learn to read you battery voltage and what it means as are as charge and you will soon learn to interpret how "empty" your batteries are.

Discussions of usable battery capacity pre-suppose that the battery(s) are in good condition and fully charged. A 5 year old battery may have less than the claimed capacity and duration when running the furnace fan and water pump or 110 volt items with an inverter. When rig is parked undriven, not connected to "shore power" batteries will "self-discharge to low levels and their useful life/capacity will be reduced. Keeping battery terminals clean and replenishing electrolyte levels with distilled water and keeping batteries charged, but not overcharged, with a 'smart" charger (Battery Minder) will prolong their useful life. Check battery voltage with a cheap digital multi-meter set on 20 volts DC scale, should read around 13.6 volts if battery is fully charged, around 14 volts with engine running.

Desert Captain wrote:
"All of which is to say that the water pump does need a non-trivial amount of current, but since it's only on sporadically for short periods of time, it doesn't consume a lot of the charge stored in the battery. "

Excuse me but isn't that basically what I posted? :h

"The water pump may be a "significant" drain but it is only on for very brief periods of time. They typically draw 5 - 6 amps {but that's per hour}. A 10 minute shower is about 1 amp. You will run out of water waaaay before you drain your batteries."

It's nice that we agree but the point we both made is exactly the same.... water pumps do not drain your battery bank.

:B

Indeed, I was not in the least bit disagreeing with your overall conclusion, but rather trying to explain the correct electrical units to use. Amps and amp-hours are measuring quite different things, and getting them mixed up or confused can be, well, confusing.

Current flow is rated in amps. Battery charge capacity is rated in amp-hours. That is Current X Time. A 10 minute shower for a 7.5A pump is 10/60 hours X 7.5A = 1.25 Amp-Hours.

If you want to get into energy, that is Current X Voltage X Time = Watt-Hours, or for your home and electric bill, kilowatt-hours. Which is also equivalent to Joules. 1 Watt-Hour = 3600 Joules.

Here is an example pump that has a current rating of 7.5A.

Shurflo Pump

The pump is of course used any time you use any water, and a big user is flushing the toilet. We have 40 gallon gray and 40 gallon black tanks so may find us toting water after a few days to refill our 40 gallon fresh tank.

We try to minimize our battery usage during dry camping and have all LED lighting. Battery life is directly related to depth of discharge, greater depth of discharge = fewer recharge cycles.

"All of which is to say that the water pump does need a non-trivial amount of current, but since it's only on sporadically for short periods of time, it doesn't consume a lot of the charge stored in the battery. "

Excuse me but isn't that basically what I posted? :h

"The water pump may be a "significant" drain but it is only on for very brief periods of time. They typically draw 5 - 6 amps {but that's per hour}. A 10 minute shower is about 1 amp. You will run out of water waaaay before you drain your batteries."

It's nice that we agree but the point we both made is exactly the same.... water pumps do not drain your battery bank.

:B

Jack (the OP),

We have a couple of these under the step in our 24V ... two of these batteries provide 230 amp hours of storage:

http://www.fullriverbattery.com/product/batteries/DC115-12

Their recommended float voltage specification exactly matches the output of our 24V's stock converter, so these batteries are not harmed by being left hooked up to the converter during storage or when camping for days on hookups.

Howdy,
I may have spoke too soon (without measuring) Regarding the Winnebago battery layout. I am hoping and assuming to ultamately use 4 Trojans. I hope they fit. But since (2) group 31 12v batteries were mentioned, that is my second choice. Sorry about the confusion

Desert Captain wrote:
The water pump may be a "significant" drain but it is only on for very brief periods of time. They typically draw 5 - 6 amps {but that's per hour}. A 10 minute shower is about 1 amp. You will run out of water waaaay before you drain your batteries.

:C

This is very confused as to what an amp is. (The overall analysis of the water pump being pretty much immaterial in terms of battery life is entirely correct.)

An ampere is a measure of current, or the rate at which electricity flows. You can think of it as being measured as electrons per some unit of time, roughly equivalent to gallons per minute for a water hose. If you get 5 gpm from a hose, that's true whether it is on for a few seconds or all day, and the same is true for electrical current.

Charge is an accumulation of current; you might think of it as a measure of stored electrons. The equivalent for water would be volume. If you are pumping water from a kiddy pool out at 5 gpm, you won't have the water level go down too much if you only run the pump for short periods of time, while a much slower leak that flows all the time could drain it if left long enough. Among other units, charge is measured in amp-hours, where one amp-hour is the charge that is moved by a current of one amp over the course of an hour. (You could measure water volume in gpm-minutes, which would of course just be gallons: one gallon per minute for one minute.)

All of which is to say that the water pump does need a non-trivial amount of current, but since it's only on sporadically for short periods of time, it doesn't consume a lot of the charge stored in the battery.

fourthclassC wrote:
Just my opinion here, which is just like most. I had 2 group 24 batteries for my coach, but removed one and the associated cables. Only because of no major long no hook up stays planned. Works fine and only one night of heater/blower use if needed. But as soon as I can get time for more travel, I am going straight to (2) 12 volt group 24 or (4) 6v Trojans. I am lucky that there is room for that many. (2003 Winnebago Mini 24V, E350/V10)

We have a 2005 Winnebago Itasca 24V Class C and the battery compartment is under the step. It doesn't look like there is enough room there for (4) 6V Trojans. We have only (2) Group 31 12V batteries there.

I'm interested in where you would put (4) Trojans in your 24V?

Just my opinion here, which is just like most. I had 2 group 24 batteries for my coach, but removed one and the associated cables. Only because of no major long no hook up stays planned. Works fine and only one night of heater/blower use if needed. But as soon as I can get time for more travel, I am going straight to (2) 12 volt group 24 or (4) 6v Trojans. I am lucky that there is room for that many. (2003 Winnebago Mini 24V, E350/V10)