Battery Life?

[jmiller12]

Newbie here. I've never boon-docked before, and was wondering how long I can have the lights on in my TT before the battery gets to a critical level (from what I've read below half way charged is bad?) I have a Winnebago Minnie, and the refrigerator and water heater can run off propane, so I am good in that department. Basically, I want to know when I pull into a Wal-Mart parking lot for the night, can I have three or four overhead lights on for a few hours and be fine? What about a day or two? If I left a light on accidentally over night would it drain my battery completely? Is there a way to measure this other than the battery meter in the TT which I have read is not an accurate reflection of battery load or the water tanks for that matter. My TT only has one battery, and I have no idea how long it can power certain loads. This is all assuming I start with a full charge because I will have been towing for a few hours and my truck is recharging the battery. Thanks

[rbpru]

There is a big big difference to stopping for a couple of day without power and boondocking.

Most anyone and squeak by for a few days on the battery or give it a 15 minute boost with a set of jumper cables off the truck.

True boondocking means the management of all resources; battery, gas, and water are the most obvious. Most serious boonedockers are geared up for it.

[Sam_Spade]

pianotuna wrote:

Deep cycle 50% recharge to 100%

AGM 12 volt 50% recharge to 100%

AND....it is useful to know that 50% discharged puts them at something very near to 12.0 volts.

Mine sometimes go a bit below that....but I don't panic because obsessing over it and modifying your whole set of power equipment in an effort to prevent it is just NOT worth the trouble.

Maybe your batteries will only last 4 years instead of 5. Big deal.....NOT.

[pianotuna]

Westend,

Marine 20% recharge to 100%

Deep cycle 50% recharge to 100%

AGM 12 volt 50% recharge to 100%

LI 80% recharge to 90% There are some indications that 40% may be a better "low". Recharging in low temperatures is not possible. Cells expand in size as they discharge. If 40% to 90% is the goal, then we are back to 50% usable capacity. So the advantages are speed of recharge, no need for 100% recharge, and weight. Disadvantages are price, cold weather operation not possible and NO forgiveness.

For high draw inverter use 12 volt jars have a slight advantage regarding voltage drop under load. It has to do with cell count, which is double that of the same capacity 6 volt battery.

My ultimate battery pack would be 48 volts @ 250 amp-hours created from 2 volt cells using the technology from "Firefly" jars. Disadvantage cost, and weight. Recharging to 100% once every (say) ten cycles would be a good plan.

[westend]

For you folks that know about this stuff, what is the lowest that you should ever let a battery be discharged to? Before permanent severe damage is done?

That differs by type of battery and construction. Typically, a dealer will equip a trailer with an inexpensive 12V marine-starting hybrid, many of them are BCI GRP24. This type of battery will last longer if never drawn down below 50%. A 12V FLA auto battery will fare even worse. Draw it down below 50% a few times and it will be very limited in capacity or toast. 12V AGM batteries fare better from high draw but the 50% rule of thumb is best. Two 6V in series connection will fare the best of high draw down because the cells are constructed better than typical 12V batteries.
Lithium batteries can be drawn down to 10% of their operational capacity but if allowed to go lower, may not survive.
Summary: 50%

[Old_Islander]

I must admit, I ruined a 105 Amp Hour RV battery, not understanding this stuff. At home, I keep the camper plugged into a 110 AC power supply to keep the battery topped up. I have a timer on the extension cord, so the camper has shore power 3 hours per day.

Then last summer, somehow the timer was disabled and it was at least two weeks before I noticed. Went out an put a meter on the battery -- 0.0 volts! 😮

Got the shore power back on and the battery recharged and seemed to hold a charge without any load. But as soon as we spent a night or two on the road with no shore power, the battery fell rapidly, requiring long charges each day with the genny.

I've replaced it and will never let anything like that happen again. I now fully charge the battery and then disconnect it, during longer periods with no use.

For you folks that know about this stuff, what is the lowest that you should ever let a battery be discharged to? Before permanent severe damage is done?

[Brassica]

SoundGuy wrote:


The OP is a newbie and won't have any idea what you mean by "dew point heater on the fridge". Explanation - many gas absorption fridges will have a 12 vdc heating element located in the area between the fridge and freezer sections that's intended to help reduce the build up of condensation when it's really humid. When on shore power leaving this heating element powered is obviously a non-issue but when running on battery power it's unnecessarily drawing down your precious battery reserve. ... we could probably tell him whether he has a heating element that can't be turned off. We could also further advise him how to install his own switch so he can disable this heating element, as necessary. ...

Well said, Sound Guy! I became aware of the dew point heater while my battery was aging and not charging well. I pulled the fuse and measured the current across the contacts. I saw 1.3 amperes as a constant load on the circuit. I read the Dometic refrigerator schematics. I could cut the wire from one particular "test point" and deactivate the heater. I would have to rewire the refrigerator light because the light and the heater are sourced from the same the test point.

Now I am shopping for a new deep cycle battery.

[2112]

My experience is a single 90AH group 27 battery will allow us to watch TV using a 100W MSW inverter for a few hours and run a small 12VDC fan in the bedroom all night. We turn a light on when needed, use the water pump sparingly when needed and have the fridge on propane with the heat strip enabled. The battery measures ~12.2V in the morning. Your experience may differ.

[BarabooBob]

Many refrigerators require 12 volt power even when running on propane. They have a control panel that turns the propane burner on and an electrical ignitor. I upgraded my truck wiring to an 8 gauge wire running from the power distribution box under the hood straight to the battery on the TT. I have not driven it since completing this modification so I don't know how it works yet.

[theoldwizard1]

jmiller12 wrote:
This is all assuming I start with a full charge because I will have been towing for a few hours and my truck is recharging the battery.

BAD ASSUMPTION !

Read this DC-DC battery charging

[profdant139]

Battery management may seem daunting and tricky. It isn't, but there is a bit of a learning curve. Hang in there! It is really worth the effort. Get a cheap multimeter and learn how to read the voltage of your battery. (It is easy!) Monitor it carefully, at first, until you get a feel for how your usage pattern affects the battery.

One key tip -- let the battery rest for at least 15 min before taking a reading. The reading you get while the battery is being used is artificially low. Once it rests a bit, the reading will reflect the true state of affairs.

[time2roll]

Yes with a single battery in good shape you should last one night without much trouble. Very easy if the lights are LED. If you run one night light you still be fine especially if it is an LED. Although probably not needed in a city parking lot if you leave a blind open a bit.

[SoundGuy]

prichardson wrote:
What size battery? Can you turn off the dew point heater on the fridge? If the first question is Grp. 24 and second is no then 1 maybe 2 nights. If you can turn off the fridge heater and minimize the number of lights then 2 to 3.
Increase the battery size and time will be longer.

The OP is a newbie and won't have any idea what you mean by "dew point heater on the fridge". Explanation - many gas absorption fridges will have a 12 vdc heating element located in the area between the fridge and freezer sections that's intended to help reduce the build up of condensation when it's really humid. When on shore power leaving this heating element powered is obviously a non-issue but when running on battery power it's unnecessarily drawing down your precious battery reserve. Obviously under those circumstances you want to turn it off, the problem being that in recent years fridge manufacturers have deleted the switch necessary for this purpose. Unfortunately the OP hasn't provided any information as to which trailer his has nor which fridge, for if we knew we could probably tell him whether he has a heating element that can't be turned off. We could also further advise him how to install his own switch so he can disable this heating element, as necessary. Until the OP offers more pertinent information as to just which battery he has, details his intended use, and offers specifics about his trailer it would be impossible for anyone to offer any reasonable answer to his original question. :R

[rbpru]

How long does I can of pop last? As long a it takes you to drink it.

It is the same with your battery. It's life depends on your use.

Our TT with it's original battery will last us two or three days if, we turn off the antenna preamp, switch the frig and water heater to propane after we changed to LED lights. We know the voltage is low when the water pump will not build enough pressure to shut itself off. The water pump is our biggest current draw.

Left in the yard the phantom loads will drain our battery in about a week or so. When we expect to Boonedock for a few days we carry an extra battery in and old picnic cooler. I have managed to stay an extra day or two by charging the battery with a set of jumper cable of the truck. It is kind of a crude approach but work if necessary.

If you intend to Boonedock you gear up for it.

We have a 25ft. TT with no special inverters etc. for 120 volt operations.

Good luck

[Sam_Spade]

In addition to the other comments, it depends in a LARGE part upon how old the battery IS; that is, whether it is really healthy or mostly worn out.

If your present "battery meter" is just a group of lights, then an actual digital voltmeter would be a HUGE help.

Bottom line: Your just going to have to try it and see. A "trial run" parked somewhere near home is always a good idea.