Can I use a deep cycle battery?

[Jon87V20]

Hello, everyone:

My wife uses a bi-pap to sleep with every night.We're currently road-tripping in our '87 Chevy Suburban V20.

The battery that's in there now, has been able to handle running the bi-pap each night just fine as long as she doesn't have the humidifier on (if she does, the machine shuts down in a loop from low voltage) and the truck has been starting just fine for about a month until today. It still starts but is cranking very slowly and I'm concerned it may not be able to start when we're  way out someplace with no cell signal because we've been camping out on logging roads etc here in Washington.

I read recently that deep cycle batteries tend to take more kindly to frequent heavy discharging than conventional vehicle batteries. Is this true?

Can I replace my battery with a marine/deep cycle type battery and expect it to work better powering the machine as well as handling starting duties for the truck in tandem?

I would ideally like to buy another battery for the truck, then in addition pick up a separate battery that would handle running the machine exclusively and maybe swap them out while driving to allow the deep cycle to charge. That way, I'd be able to ensure I could start the truck. However, there's no way I can afford to buy two batteries at this time.

Any advice or ideas?

Thanks!

[Irish_Alley]

i cant help with tech information but i know in my mud truck at one point had a deep cell. i would let her sit a month and charge it or try to charge it and it didnt last.
i did pick one of these up


for 100 or so. if you were a few states closer i wouldnt mind letting you test it to see if it can keep up for a day.

bd and them will chime in and be able to tell you how to rig dual batteries up so you only pull from one but while charging you charge both.

[bd]

...However, there's no way I can afford to buy two batteries at this time....

Therein lies the limiting factor.

If the existing cranking battery is worn out and you need to replace it, by all means install a dual-purpose, deep cycle battery, such as an Optima Yellow Top.  They are specifically designed for the dual usage you describe (cranking plus repeated deep discharge from powering accessories).  But, the price... YIKES!  And, you still face the problem of not cranking in the morning if the battery is discharged too far.

Your optimum solution is to employ two securely mounted batteries that are electrically isolated during use, yet charge simultaneously while the engine is running - a conventional battery for engine cranking and a deep-cycle battery for accessories, both connected to the alternator using an isolation relay or diode isolator.  Once installed, operation would be virtually seamless and trouble free.  But, that's not easily accomplished while traveling and camping on a tight budget.

The equipment shutting down when it senses a predetermined drop in voltage is a unique problem.  For uninterrupted use throughout the night, you need to provide a consistent voltage source: either a bank of batteries cabled in parallel that will recharge while driving, a gas powered generator, an RV park with power hookups or a motel.  A dubious alternative is to let the engine idle all night, which can expose you to serious risk of deadly carbon monoxide asphyxiation - a silent killer!

In any case, IMHO a portable power pack for emergency jump-starting is essential if you are traveling solo into remote areas with poor cell phone service and/or accessibility.

[Jon87V20]

Ok well maybe I'll just have to splurge a bit and pick up two batteries. Do you have a link for a good write-up on how to charge both but pull from one? I feel like I tried to Google that a while back and couldn't find a good guide on that. Thanks!

[Irish_Alley]

i will also say good things about optima batteries. when i worked at autozone prob getting close to 12 years now. some guy came in with a "dead" optima and he couldnt get it to hold a charge. it had some age on it but it was an optima and we took it as a core charge. but we had some other batteries people just gave to us so they wouldnt have to hold on to them. and i swapped it out with another battery, i then left it on trickle charge all night. the next day i put it into my truck and to this day shes still going strong. so i have 12+ years on a optima red top

[big_al273]

i don't know where the wiring diagram would be off the top of my head but my truck has the slide in camper prep option and stock wiring of the second (drivers side) battery is through cut off relay mounted to the fender that connects the battery to the rest of the vehicles electrical system ONLY when the key is turned on, from what i've read the second battery was meant to be a deep cycle and was for powering a slid in camper without killing the main battery while parked, i just ran a cable across the rad so i have dual cranking batteries instead, although the relay and wiring is still there and tucked away on the inner fender

[Irish_Alley]

i know BD has posted a diagram on here before about it. ill take a look

[Dr_Snooz]

Your ideal solution is to buy a second deep-cycle battery and connect it via a battery isolator.



https://www.amazon.com/Cole-Hersee-48120-Battery-Isolator/dp/B001FQOGFS?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duckduckgo-d-20&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B001FQOGFS

It's a very common problem in the RV community where you want to discharge one battery (in the RV) while preserving the starting battery (in the truck). The isolator isolates the two batteries until the engine is running, then allows both batteries to charge.

It's not the cheapest solution, but it is the right one.

[fitz]

  You could wire it up like a boat.  2 batteries wired in parallel with a selector switch wired between the (+) cables.
  The switch (about $40) will let you charge both batteries while driving.  At night you can run accessories of battery #1 or #2.  This leaves the other battery disconnected.  In the morning just flick the switch and you have 1 fully charged battery waiting to start your truck.

[fitz]

Here's the switch.

[VileZambonie]

A guy I worked with went camping all the time and wanted an auxiliary deep cycle battery. I simply wired it in parallel with an on off switch and a wing nut for the hold down and wing nuts for the terminals. The charging system recharges the aux battery, it serves as a backup battery and easily comes in and out of the battery tray to power other items like a trolling motor, etc. Very easy to do.

[Jon87V20]

Thanks for all the great info and help, everyone!

I ended up ordering one of those Optima Yellow Top batteries today (D75-25). The local parts shops were charging about $240 give or take. However, I was able to find one on Amazon for $184 and we had an unused $50 Amazon gift card we put towards it as well so we're definitely getting a deal on it.

Sometime down the road, I'll probably go the dual battery route when I have the money. From what I've read here and elsewhere, these yellow top Optimas sound pretty tough, so I'm optimistic it will do the job for us for now.

Now I'm on to the next issue. I went out yesterday and saw that coolant was steadily dripping down the lower radiator hose on to the ground. Oddly enough, I filled the radiator back up, drove it in to town and since I've come back it's no longer leaking. Radiator's still full. Kind of strange. I'll be picking up a new hose anyway.

[big_al273]

Ok it's not a wiring diagram but it's pretty simple: first picture shows where the main connection to the B+ junction block beside the master cylinder, the wire goes to the relay on the fender. Second photo shows the signal wire for the relay going through a grommet into the cab under the main wiring harness plug.
pictures are being a pain today standby more pictures in part 2

[big_al273]

Part 2
Third photo shows the relay and on the left behind the wires coming off the relay you can see the edge of a power junction block, this block is connected to the isolated battery side of the relay so i assume it is the factory power point for the slide in camper or other accessory as it is always connected to the isolated battery. Forth photo shows the isolated battery positive cable (not in use in my truck as previously stated). Fifth photo shows where the signal wire from the relay is plugged into the fuse block on one of the accessory sockets so the relay energizes whenever the key is in the on or accessory position. You should be able to duplicate this setup with off the shelf components, hope this helps

[Jon87V20]

Thanks for that info Big Al.

Not sure what's going on. I put in that new Optima Yellow Top and it's still cranking over very slowly. The ground strap from the battery to the firewall looks like it's fine. Nothing else electrical has been acting up other than it keeps popping the "power acc" fuse which kills my door locks and the key switch to operate the window in the tailgate (switch on the dash still works).

The other posts I've read are all saying it turned out to be the starter. I know timing can affect cranking but I've never messed with the timing and this truck and it's not pinging or getting hot.

I guess I'll try buying a starter and see if that helps.

Any other ideas?