Aftermarket alternator?

[Terrymo]

For me, the biggest advantages of the Genesis dual battery system were increasing the total battery capacity and eliminating the difficult-to-access OEM motorcycle battery. Isolating the accessory battery made sense to me too, but if everything else is working properly that matters much less. The “jump start“ feature is worthless to me, as it hasn’t worked in the past and it’s easy to carry a little jump-pack. If the set-up you describe here would work, that would be great.

Combining the batteries yourself worked either with an in cab switch or simply by manually latching the magnetic relay with a yellow lever on top of the MLR. But once the primary battery came up to a certain state of charge you could hear the relay latch as the secondary battery started charging. Like I said, it was simple and understandable for me.

But in my scenario you went from one 34/78 battery to two using a preexisting second battery tray because the tray was already there but empty on some years. So in that scenario you did get a true accessory (house) and worthwhile back up battery. On the JL we just don’t have the same kind of room.

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[THAW]

Ok so next question which you may have answered for me once already regarding a JL. Why not a dual battery set up with a Blue Sea magnetic latching relay charged by a dual bank Noco or similar?

i thought the value of a dc to dc charger was to eliminate large capacity wiring to a remote battery. What is the advantage to a DC to DC charger with two batteries right next to each other over a Blue Sea ACR or MLR?

My brain really liked the dumbness of the set up, and my OCD the visual simplicity. I suspect a 2000 GMC Sierra 4x4 and the more modern JL have different charging requirements while driving,

So the Genesis gen 2 and 3 hubs use the same kind of technology/logic as Blue Sea charging relays. The idea behind the single-bank AC/wall charger connected to the crank battery is the charging relay handles the auxiliary battery connection just as it does for the alternator.

To use a dual-bank AC/wall charger, a charging relay obviously has to be manually locked in the battery-separated state (or disconnected altogether if it doesn't have that feature, which the Genesis gen 2 doesn't); a manual locking requirement might defeat the purpose of the "Automatic" in "Automatic Charging Relay". In any case, there may or may not be benefit to charging the batteries separately, but either way a dual-bank AC/wall charger doesn't fully address the underlying problems created by switching batteries in and out of parallel in various other charging/discharging conditions.

Enter DC-DC chargers. There are a couple reasons to use a DC-DC charger (which the latest Genesis systems do), wherever the location of the second battery. First, vehicle alternator systems aren't ideal chargers, especially for deeply-cycled batteries; they're inherently constrained by other vehicle operation priorities (e.g. fuel conservation strategies). In the case of the JL, only one of the batteries - not the entire bank - is fully monitored by the IBS. Second, pulling AGM batteries in and out of parallel at different SoCs stresses them and creates mismatched internal resistance which leads to parallel charging issues that contribute to shortened battery life. Put simply, DC-DC chargers are a modern, more effective method for adding an auxiliary battery to a vehicle - but particular cases an Automatic Charging Relay fits may still exist.

By the way, one also has to consider the effects of an attached DC-DC charger when using an AC/wall charger; if the DC-DC charger has a higher Amp-rating than the AC/wall charger and doesn't have an ignition switch, the DC-DC charger could fully drain the crank battery while the AC/wall charger attempts to charge it.

 

[Terrymo]

So the Genesis gen 2 and 3 hubs use the same kind of technology/logic as Blue Sea charging relays. The idea behind the single-bank AC/wall charger connected to the crank battery is the charging relay handles the auxiliary battery connection just as it does for the alternator.

To use a dual-bank AC/wall charger, a charging relay obviously has to be manually locked in the battery-separated state (or disconnected altogether if it doesn't have that feature, which the Genesis gen 2 doesn't); a manual locking requirement might defeat the purpose of the "Automatic" in "Automatic Charging Relay". In any case, there may or may not be benefit to charging the batteries separately, but either way a dual-bank AC/wall charger doesn't fully address the underlying problems created by switching batteries in and out of parallel in various other charging/discharging conditions.

Enter DC-DC chargers. There are a couple reasons to use a DC-DC charger (which the latest Genesis systems do), wherever the location of the second battery. First, vehicle alternator systems aren't ideal chargers, especially for deeply-cycled batteries; they're inherently constrained by other vehicle operation priorities (e.g. fuel conservation strategies). In the case of the JL, only one of the batteries - not the entire bank - is fully monitored by the IBS. Second, pulling AGM batteries in and out of parallel at different SoCs stresses them and creates mismatched internal resistance which leads to parallel charging issues that contribute to shortened battery life. Put simply, DC-DC chargers are a modern, more effective method for adding an auxiliary battery to a vehicle - but particular cases an Automatic Charging Relay fits may still exist.

By the way, one also has to consider the effects of an attached DC-DC charger when using an AC/wall charger; if the DC-DC charger has a higher Amp-rating than the AC/wall charger and doesn't have an ignition switch, the DC-DC charger could fully drain the crank battery while the AC/wall charger attempts to charge it.

Ok good info as always and at an understandable level. Thank you.

 

[Whaler27]

Combining the batteries yourself worked either with an in cab switch or simply by manually latching the magnetic relay with a yellow lever on top of the MLR. But once the primary battery came up to a certain state of charge you could hear the relay latch as the secondary battery started charging. Like I said, it was simple and understandable for me.

But in my scenario you went from one 34/78 battery to two using a preexisting second battery tray because the tray was already there but empty on some years. So in that scenario you did get a true accessory (house) and worthwhile back up battery. On the JL we just don’t have the same kind of room.

The only advantage of the Genesis conversion is I DO have the room and a second battery ready to participate! If that’s all my expensive investment bought me it’s a lousy deal, but I’m looking for the silver lining to my cloud wherever I can find it…

 

[Terrymo]

The only advantage of the Genesis conversion is I DO have the room and a second battery ready to participate! If that’s all my expensive investment bought me it’s a lousy deal, but I’m looking for the silver lining to my cloud wherever I can find it…

Room for two batteries the size of the OEM?

 

[THAW]

The only advantage of the Genesis conversion is I DO have the room and a second battery ready to participate! If that’s all my expensive investment bought me it’s a lousy deal, but I’m looking for the silver lining to my cloud wherever I can find it…

If you exclude the price of the Genesis DIY Kit battery tray from the Genesis Gen 3 Dual Battery System base price, the charging relay and wiring cost $500. That's a little expensive, but it's not totally unfair for a robust, custom-footprint, plug-and-play automatic charging relay system. [I hear you on the need for previous-customer upgrade special pricing.]

The fact a $400 start battery is required to run the Genesis system because of the different group sizing also increases total consumer cost, but that's the tradeoff for fitting a dual-battery system in the crowded JL engine bay.

Another benefit of using a DC-DC charger that I forgot to mention earlier is: because the batteries don't live and die together, they don't have to be replaced at the same time. The start battery replacement schedule follows the normal JL interval, while auxiliary battery replacement isn't strictly necessary and is based only on cycle requirements and charging maintenance. And, it's even possible to switch auxiliary battery chemistry - though the jury may still be out on LiFePo4 batteries living in a hot engine bay.

 

[Whaler27]

Room for two batteries the size of the OEM?

No. I have the Genesis system, so I have the batteries that fit that tray.

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