Secondary or Tertiary backup battery? How paranoid are you?

[XERTYX]

Has anyone considered the event of and or eventuality of an uncharged house battery unable to provide obligatory household functions such as but not limited to and or manageable without or without electricity as determined by circumstances etc? 

°Indoor LED lighting. 
°Emergency Circuitry such as Cabin Phone charger
°CPAP / medical equipment etc

Does your system have redundancy? 

Secondary redundancy? 

Best backup battery solutions and methods of charging / maintaining such batteries? 


When I lived aboard a floating vessel I had a solar bank of AGM batteries salvaged from a large UPS (uninterruptabke power supply) that fueled my world. I refer to that phase of my life as "when I was a solar farmer".

Lights were accessible via the cabin 12V supply, the AGM battery bank, or NICad batteries I had installed that I salvaged from a 12V "sawzall" type clone I used to make additions to my ship. I used the NICad lighting most of the time. I recharged the bank from a hand crank flashlight generator I got at goodwill for about a dollar.

As you can see I'm quite paranoid. 

Are you? 

How do you squirrel away power for a rainy day?  (Pun intended)

 

[Gr8ful]

Diesel with 2 large 12v batteries & a device that lets the 250 amp altonater charge the starting & house batteies but will never let the starting batteries drain, a generator & battery charger also. It I were going to use power tool batteries I use the 40v ryobi's.

 

[Wabbit]

I'm more aware than I am paranoid. I have my 215ah battery bank charged by solar or a generator if the clouds set in for a few days. I keep an eye on my battery bank performance and when it degrades to a certain point I will replace it. The bank consists of 2x 6v golf cart batteries. These batteries can be replaced in almost any decent sized metropolitan area. No need to carry a backup set as I'm usually never more than an hour or so from a bigger city.

I do have a small 10000mah portable power pack that I keep around in case I go out and about for a day to recharge my phone if need be, but that's about it.

 

[MrNoodly]

The only critical electrical thing I have is my small fridge. If I lose power then, eh, I lose a few bucks of perishable food. I could cope. And since I'm not at sea, alternatives and solutions are easily at hand.

Rather than spend money up front for backups I may never need, I prefer having a reserve fund for when things actually go wrong.

 

[B and C]

No extra backup batteries here either unless you count the engine battery. I have 375 Ah of AGM UPS batteries as my house bank and mainly charge from solar or driving (battery isolator). I also have a generator for when there are several days of bad weather. My battery bank is going on 8 years old and is losing capacity so I will need to replace them sometime in the near future. If they were to go completely flat, I could plug my CPAP machine into the chassis battery power port in the front for a night and then go get new batteries. I don't use a humidifier so drain on the battery is minimal. I bought the 12V plug for my CPAP so no inverter required.

 

[Trebor English]

I don't have any critical needs for electricity.  I don't use a CPAP, I don't have a kilobuck of perishable medications in the fridge and I don't need anchor lights.  

I have one group size 24, $80, 75 amp hour trolling motor battery.  It starts the engine and runs my fan at night.  I have no jumper pack, lithium or lead acid.  

I have a fancy volt meter that can show the minimum voltage over a period of time.  When starting the engine the battery voltage now goes down to 7.6 volts.  It used to stay over 9.  The water consumption has been 20 to 30 ml per cell per month.  That is now up 50%.  The battery is 2.5 years old.  

I expect that my battery will fail due to an open circuit in one cell.  I have consistently overcharged the battery and the hydrometer indicates that the gradual loss of capacity due to sulfation is not an issue.  

The only reasonable backup in this situation would be to buy the replacement battery and either A) have it on hand when needed or B) have it already installed.  There is no jumper pack that can substitute for a battery that is disconnected by an open circuit.  

My main concern is that the battery will fail while driving.  Disconnecting the battery while the alternator is charging can result in a high voltage pulse that can ruin everything plugged in at the time.  The huge starter current is more likely to cause the failure and that will cause no additional damage like the alternator load dump would.  

My plan is to replace the battery when the voltage minimum while cranking gets down to 7 volts.  That would indicate more resistance in the battery due to more corrosion.  Most vehicle electronics need 5 volts to operate so they need 7 volts input to their regulator circuits.  So, 7 volts then plan B, new battery already installed.

 

[rvwandering]

Our batteries are charged with solar and by driving - easy enough to take a drive if our batteries were drained to the point where we didn't have enough for lights or charging small devices. This has never happened even though we're hard on our batteries and have taken them down way below recommended levels. We lose our 110 power when the voltage is too low but we can still use our 12-volt system for lights, water pump, etc.
So, no, we're not paranoid but then we're not out in the middle of the ocean far from any supplies or fast help.

 

[jonyjoe303]

I have my 220ah lifepo4 house battery, a modest 65ah li-ion battery and also a smaller 27ah li-ion battery. And I keep a 28ah agm as a jumpstart battery in case my cranking battery won't start. I charge everything with my 240 watt solar panel and keep a spare charge controller in case 1 fails.

It never hurts to have an extra battery.

 

[Weight]

Going onto the water with used batteries? You do need backup. My bank is over designed for what I estimated my energy use plus recharging. I bought new battery.

 

[maki2]

I have two, a house battery for my travel trailer and one for my tow vehicle too. My tow vehicle is my backup camper and guest bedroom. If I want to leave the trailer at a campsite, go into town and need to do work on my computer for business or work while laundry is cycling through machines then it works for that as well.

 

[Seminole Wind]

i feel pretty secure with multiple charging sources, solar, engine and stand alone pull start generator. my house bank is modular with 4 golf cart batteries. should one or even 2 fail unexpectedly i can rewire and just have a smaller bank till i can replace. in a complete house bank failure i could run my critical needs off engine start batteries till i could find replacements and just supplement charging via engine or generator. no worries of being stranded with dead batteries and unable to start my rig as i can use the house bank to help start if the starting batteries some how go flat and i can always pull start the honda and charge with the stand alone 30amp constant current battery charger. if the SHTF so bad that all those redundancy and contingencies run out. i am sure there will be far more pressing things to concern myself with then a little electricity. like do i have enough ammo to survive the night against the zombies...

 

[WalkaboutTed]

My question is, if you can't keepthe primary batteries charged all the time, how would you keep the secondary or tertiary battery banks charged?

No backup batteries on the trailer. We've boondocked for months and have never taken them down more than 25%. They get only solar. Both vans have battery banks, though, I guess you could call them secondary battery backup banks. Both banks are charged by solar or the alternator. But both vehicles have been left unattended for months, while running the fridges 24/7 in each van. They have the engine batteries, but we don't worry about them as we can use the battery banks to jump ourselves (that sounds faintly obscene, no?).

After we put the solar on the trailer, we never had to use the portable solar again. Nor have I used my baby Ryobi generator. If your system is designed well, you should be fine.

But, on small sailboats, the alternator may not be able to work hard enough to keep a bank charged. And shrouds and lines will interfere with solar (more so if you're friggin' in the riggin'). Put your numbers up here to get more accurate suggestions from other members.
Best wishes with your build,
Ted