I've been thinking about adding a dual battery system to my truck, but I'm curious how much difference there can be between batteries. The primary battery for my truck is this: odyssey 27F a 27f battery that has 930 CCA, and a 88 AH capacity. I also have a battery from a car I have in long term storage, that I was thinking could pull double duty as a second battery in my truck instead of just sitting endlessly on a charger. That battery is this: odyssey 35 a group 35 battery that has 675 CCA, and a 55 ah capacity. Now I'm thinking if I use a dual battery system that ties the batteries together using the alternator to charge them, I will have issues, as the lower capacity battery will "set" the maximum charge for the system. However, if I use a DC-DC charger like redarc offers, that uses one battery to charge the other, I should be ok...Is this correct or am I wrong on how this works?
How close in Spec do dual batteries need to be?
- Thread starter dra2120
- Start date
DiploStrat
Expedition Leader
At 90 MPH.
When under charge, the batteries just have to be grossly of the same type, e.g. lead acid or lithium. (Assuming that the charge profile is correct.)
When combined in the same bank, the batteries should be identical. Better if from the same production run, etc.
If separated when discharging, doesn't matter.
A decent B2B, e.g. Sterling, REDARC, etc. will provide complete isolation and will allow you to select the appropriate profile for the second battery.
Worth noting that, assuming that you want the second battery for camper use, a starter battery will not perform as well, or last as long, as a true deep-cycle battery.
When under charge, the batteries just have to be grossly of the same type, e.g. lead acid or lithium. (Assuming that the charge profile is correct.)
When combined in the same bank, the batteries should be identical. Better if from the same production run, etc.
If separated when discharging, doesn't matter.
A decent B2B, e.g. Sterling, REDARC, etc. will provide complete isolation and will allow you to select the appropriate profile for the second battery.
Worth noting that, assuming that you want the second battery for camper use, a starter battery will not perform as well, or last as long, as a true deep-cycle battery.
Yes a proper House bank should comprise a completely different kind of battery, specifically designed for deep cycling
than what you would choose for a vehicle Starter batt.
There just needs to be a point of voltage overlap between their profile specs, to set the charge sources to.
Best practice is optimizing for House to be well coddled, Starter being cheaper, less fussy and usually never drawn down more than a few percent SoC.
than what you would choose for a vehicle Starter batt.
There just needs to be a point of voltage overlap between their profile specs, to set the charge sources to.
Best practice is optimizing for House to be well coddled, Starter being cheaper, less fussy and usually never drawn down more than a few percent SoC.
jonyjoe101
Adventurer
Both batteries are oddessys, I would just connect them together. They both will equalized and when you charge them, the one that is full will stop accepting amps while the other one will still keep charging. Thats what I see when I parallel different type of batteries.
I connected many different type of batteries together in parallel with a dc wattmeter in between so I can see how much amps go between one battery to another. At most 1 or 2 amps get transfered, once the batterys equalize no amps get transfered. I even connected my 220ah lifepo4 to my intesrtate lead acid start battery, after leaving connected all night long about 2 amps get transfered from the lifepo4 to lead acid until they equalized. The weak battery won't drain the strong battery. I never seen that happened but it could if one battery is defected.
2 batteries connected together at about the same voltage, you won't see any large amp transfer between batteries, you only start seeing large amps (over 5 amps), when the voltage starts climbing to 14 volts or higher (charging).
An example would be when I'm charging a 102ah agm house battery with solar, once full it will float at about 2 amps, now I decide to connect a smaller 27ah agm thats half full to the solar system, all of a sudden the solar controller starts putting out 12 amps to charge the 27ah agm, at the same time the 102ah battery still connected is still float charging.
The only thing about odesseys, you need to everyonce in a while top them off to 14.7 volts to fully charge (something the alternator never does). I have a fullriver agm (clone of the oddesy) as a start battery that also requires 14.7 volts. If I don't top it off every other day to 14.7 volts (with dc-dc charger) I start getting slow cranks. The oem chargers that oddesey sells for its agms charge the battery to 14.7 volts, the specs for the batteries doesnt really specify what the charge rate should be (between 14.2 to 14.8 volts as per FAQ's). I do believe charging the oddessys to 14.7 volts will make the batteries last longer. My fullriver agm is at least 8 years old and still going strong.
I connected many different type of batteries together in parallel with a dc wattmeter in between so I can see how much amps go between one battery to another. At most 1 or 2 amps get transfered, once the batterys equalize no amps get transfered. I even connected my 220ah lifepo4 to my intesrtate lead acid start battery, after leaving connected all night long about 2 amps get transfered from the lifepo4 to lead acid until they equalized. The weak battery won't drain the strong battery. I never seen that happened but it could if one battery is defected.
2 batteries connected together at about the same voltage, you won't see any large amp transfer between batteries, you only start seeing large amps (over 5 amps), when the voltage starts climbing to 14 volts or higher (charging).
An example would be when I'm charging a 102ah agm house battery with solar, once full it will float at about 2 amps, now I decide to connect a smaller 27ah agm thats half full to the solar system, all of a sudden the solar controller starts putting out 12 amps to charge the 27ah agm, at the same time the 102ah battery still connected is still float charging.
The only thing about odesseys, you need to everyonce in a while top them off to 14.7 volts to fully charge (something the alternator never does). I have a fullriver agm (clone of the oddesy) as a start battery that also requires 14.7 volts. If I don't top it off every other day to 14.7 volts (with dc-dc charger) I start getting slow cranks. The oem chargers that oddesey sells for its agms charge the battery to 14.7 volts, the specs for the batteries doesnt really specify what the charge rate should be (between 14.2 to 14.8 volts as per FAQ's). I do believe charging the oddessys to 14.7 volts will make the batteries last longer. My fullriver agm is at least 8 years old and still going strong.