Deep Cycle Battery in Pickup

[Mudfarmer]

I'm pretty sure these batteries are separated (since that's what I wanted from the installer). As confirmation, when the starting battery died a year ago, the winch battery was fine and had plenty of juice to start the engine - I just placed one jumper cable from positive to positive. I'll check with the installer for an opinion.

 

[LittleBill21]

I'm pretty sure these batteries are separated (since that's what I wanted from the installer). As confirmation, when the starting battery died a year ago, the winch battery was fine and had plenty of juice to start the engine - I just placed one jumper cable from positive to positive. I'll check with the installer for an opinion.

then your fine, if the wires go to a box or a solenoid, then they are separated. the deep cycle will be fine, and is what prolly should have been used in the first place

 

[Tx Jim]

IMHO a deep cycle battery wasn't designed for automotive use being continually attached to alternator. Deep cycle were designed for tasks such as operating a boat trolling motor which discharges battery of the majority of stored electricity & repeatedly being recharged.

I agree 12 volt batteries attached in parallel need to be equal in size & age. I've had experience with this type battery arrangement on JD tractor since 1993 when I purchased my JD 4255 tractor

 

[LittleBill21]

there is no difference between a starting and deep cycle battery other then plate design, one is designed to give large bursts of energy for short durations, the other last longer at lower usage rates. DOD or Depth of discharge determines the life cycle of a battery, 1000's of short discharges is better then a couple deep discharges, being hooked to a charging source does not hurt it, although it becomes sulfated. this will also occur with a starting battery.

 

[Thunder chicken]

One question I’d be asking is if an alternator charges at the correct voltage for the deep cycle (or an AGM type if you went that route).
I think the alternator puts out a voltage slightly lower than the deep cycle wants to ‘fully charge’ and does not have the smarts to properly cut off when it’s charged properly. You can get a DC-DC charger but they tend to be a bit pricy.

 

[rScotty]

I'm pretty sure these batteries are separated (since that's what I wanted from the installer). As confirmation, when the starting battery died a year ago, the winch battery was fine and had plenty of juice to start the engine - I just placed one jumper cable from positive to positive. I'll check with the installer for an opinion.

OK, so that answers the basic question. You have a separate battery system which is isolated as far as load goes.

So the answer to your original question is "yes", You can mix and match batteries without any problem.

The only downside is a slight one, and involves common charging systems. And only happens when one battery is a flooded cell and the other is an AGM. In that case, because most OEM voltage regulators are set to so that their output charges a flooded cell battery most efficiently, then then there is a chance that the AGM battery will not ever be fully charged.
But it will be close. Very close. My bet is that you'll never notice the slight loss.
rScotty

 

[tomplum]

My service truck uses 3 deep cycle starting batteries. 2 exclusively for the inverter and and one for engine start that can be switched for inverter use. They get switched out every 3 years.

 

[rScotty]

My service truck uses 3 deep cycle starting batteries. 2 exclusively for the inverter and and one for engine start that can be switched for inverter use. They get switched out every 3 years.

That's a good way to do it. In fact, I do it the same way.
Plus there is a manual over-ride to start it with all batteries if needed.
rScotty

 

[CausticUrbanCoast]

One question I’d be asking is if an alternator charges at the correct voltage for the deep cycle (or an AGM type if you went that route).
I think the alternator puts out a voltage slightly lower than the deep cycle wants to ‘fully charge’ and does not have the smarts to properly cut off when it’s charged properly. You can get a DC-DC charger but they tend to be a bit pricy.

Never make that assumption about alternators/generators on vehicles or tractors. They generally output 13.8V-21V, very few put out a rectified 12V or less than 12V (if they did they would never recharge the battery, they would only keep up with the vehicles power demand, or in the case of less your lights start flickering).

Older tractors are slightly different in that they usually have almost no power draw unless the lights are on. Had one tractor that needed to be disconnected after starting because it would happily boil the battery dry.

Alternators are not intelligent charging devices, they do not have the capability to properly charge or maintain batteries, and that is not what they are there for. Propper battery charging is not voltage based, it is current and temperature based.

Myself I use an inverter-charge controller inline on my RV deepcell batteries, it controls when to limit current due to battery temperature or capacity, when to shutoff supply to protect each of the batteries, and when it needs to balance.

When the batteries are out, they live on a charger that has the capability to exercise them. One could use a trickle charger, but I feel that shortens the life of deepcell/high discharge batteries.

The average, generic, non-regulated, alternator output is supposed to be around 14.5-14.8V I have always been told.

 

[alexpops]

Check your isolator/combiner to see what the voltage loss is. In boats, which often run deep cycle & starting batteries side by side for draws/joined for charging, the isolators tend to lose some voltage on the charge side due to the diodes whereas the combiners run full voltage from the alternator using a solenoid set-up. Isolator can result in undercharging & shorter life on the deep cycles & may limit the type of replacement battery you should look at (lead acid/gel/AGM). Combiners can fry your starting battery by overcharging when the Deep cycles are significantly lower in charge status unless they have monitoring & switching capabilities for the two banks. Chances are you have an isolator since they are cheaper & if you can live with reduced battery life on the deep cycle side, go for any size that will fit the space & won't overtax your alternator. You can desulfate/recondition as necessary with a good "smart" battery charger to try & extend deep cycle battery life.